The World of Computer Software/World_Of_Computer_Software-02-385-Vol-1of3.iso/e/estat21.zip/EASIDOC.ZIP/ESCHAP04.DOC

Text File | 1992-09-14 | 26KB | 794 lines

     Chapter 4: COMMAND SYNTAX

     To get EASISTAT to do anything you have to give it a
     command to perform. Most commands will also require other
     information, such as which columns to apply a particular
     analysis to. The way in which this information is
     specified can be called the format or syntax of the
     command. When each command is described in this manual
     its format is defined with it, but to understand the
     format required there are some important general rules it
     is helpful to become familiar with first.

     To illustrate these rules we will take the BASICS
     command, which is described later in the manual in the
     following way:

     Format: B[asics] [r[anks]] [g[raphfile]] column [if condition]

     This means that the command is called BASICS, but that
     all but the first letter B is optional, that it can have
     an optional switch called RANKS, that it can produce a
     graph file, that the column to be studied must be
     specified, and that finally one can add logical and
     arithmetic conditions limiting the rows to be studied by
     entering IF followed by a condition. This means that one
     can enter for instance:

     BASICS RANKS C1 IF (C2-C3)<7

     This command would cause the basic description of the
     values in column 1 to be displayed (their mean, mode,
     standard deviation, etc.), taking only those rows for
     which the value in column 2 minus the value in column 3
     was less than 7, and would also display the rank and
     frequency table of the values. In the sections which
     follow we will look at the individual aspects of command
     format more closely.


     4:1. Selecting a command

     Here is the list of commands available (it is displayed
     by EASISTAT when the HELP command is selected):

     Help                              Titles
     Basics [G] [ranks] col [if cond]  Data [save] [filename]
     List [if cond or variables]       Chisq [G] [Fish] [Num] [c r]
     Wilcoxon [S] [col]                Ttest [paired]
     Anova [G or N] [col]              Kendall's [col col]
     Kolmogorov [G] [col]              Regress [G] [col col [col]]
     Multiple regression [col [col]]   Component analysis [G]
     Minimise [expression]             Narrow cond
     Widen [cond]                      Arithmetic [expression]
     New [col or row or next]          Label [col [name]]
     Format [col or def [width dec]]   Derive [col [expression]]
     Delete [col or row or all]        Echo
     Input [filename or close]         Output [filename or close]
     Log [filename or close]           Edit
     Screen                            Sort [d[own]] [col]
     Pause                             System [command]
     Limits [cl]                       Copy [lc,tr,rc,br,new lc,new tr]
     Macro [list or label exp]         Quit

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        Command syntax

     To select one of these commands when asked simply type in
     the first part of the first word of the name of the
     command. You do not have to type in the whole word.
     EASISTAT will select the first command from the above
     list that matches the letters you have typed. So to
     select the BASICS command you could type:

     BASICS

     or:

     BAS

     or:

     B

     Note that if you type:

     W

     you will get the WILCOXON command and not the WIDEN
     command. If you want the WIDEN command you would have to
     type at least:

     WID

     Remember eveything can be typed in upper or lower case,
     or a mixture. So:

     b

     is just as good as:

     BASICS

     To use the same example given above, one could type:

     B RANKS C1 IF (C2-C3)<7

     or:

     bas ranks c1 if (c2-c3)<7

     and achieve just the same result.

     When the format of a command is described in this manual,
     square brackets are put round the optional letters of the
     command name, e.g.:

      B[asics]
      Wid[en]


     4:2. Command options

     Some of the commands can have different options attached
     to them. An option appears in square brackets in the list
     above and when the manual describes each command. An
     option can be selected or not, and sometimes more than
     one option can be selected. BASICS has an option, RANKS,
     which makes it print out a list of values in rank order

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        Command syntax

     together with values for rank, percentage and cumulative
     percentage. An option can often be abbreviated down to
     the first letter, although the whole word can be typed
     for clarity. Taking the above example one could enter:

     BASICS RANKS C1 IF (C2-C3)<7

     or:

     b r c1 if (c2-c3)<7

     If the "r" is left out, the BASICS command will do
     exactly the same thing but without also producing the
     rank/frequency table:

     b c1 if (c2-c3)<7

     If the option to produce a graph file is selected then a
     file containing data to produce a frequency histogram
     will be written to disk and EASIGRAF will be run to
     display the graph:

     b g c1

     The final option available in BASICS is IF followed by a
     condition which specifies which rows to study. IF is
     exceptional in that it must be written in full, just "I"
     would not be adequate. This option similarly can be left
     out, in which cases all the rows will be included in the
     analysis:

     b c1

     or:

     BASICS C1

     When using the BASICS command it is obligatory to specify
     the column for which the statistics are to be provided.
     For some of other the commands a column or filename is
     shown as being optional by being put in square brackets.
     This means that you do not have to type the column in the
     command line, but then you will be asked by EASISTAT to
     specify which column you mean in a second line. It's just
     a question of convenience for you whether you put the
     column into the command line or not. When you first start
     to use EASISTAT it is better just to select a command and
     then EASISTAT will ask you for other details, but as you
     grow more familiar with the program you may feel like
     typing more into the first line. There is an important
     point however. Although if you omit a necessary parameter
     like a column number you will usually be asked to supply
     it, in contrast if you omit an option like RANKS or IF
     from the command line you cannot add it in later in a
     second line. All the command options must be specified in
     the command line.


     4:3. Referring to entries in
     the data table



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        Command syntax

     EASISTAT is based around the concept that there is a
     table of values with all the different measured variables
     attached to one data object (eg an experimental subject)
     are in one row, and that they are arranged in columns
     according to the quantity they measure. So one column
     might be for temperature, another for mass, etc. and one
     row might be for one rock and another row for another.
     Thus the statistical commands essentially operate down
     columns rather than across rows - the mean of one rock's
     weight and temperature would make little sense.

     In almost all commands we need to be able to tell
     EASISTAT which columns we want to look at and one way to
     do this is to type C followed immediately (no space) by a
     number between 1 and the number of columns there are,
     e.g. C1, c3, c25. We used this syntax in the example
     above when we said:

     b c1

     meaning calculate the basic statistics of all the values
     appearing in the first column. Occasionally we may wish
     to refer to a specific row - when we want to delete a
     certain row perhaps. To do this we type the keyword ROW
     followed by a space and then the number of the row we
     mean, e.g. row 4, ROW 29.

     Every column of the table also has a label, which appears
     at the top of the column in the data file and when using
     the data editor. This would usually describe what it is
     that the values in that column are measures of, such as
     AGE or SEX. These labels can also be used to refer to the
     columns so that if the second column is labelled AGE then
     the following both mean the same thing:

     BASICS AGE

     BASICS C2

     In the logical and arithmetic expressions described below
     it is necessary to refer to the values which appear in
     cells in different rows. The rows are looked at one at a
     time and then the value specified is taken from that row,
     so that in a logical expression c15 means "the value
     appearing in column 15 of the row I am currently
     interested in". In this context the keyword ROW (here
     appearing with no number after it) means "the number of
     the row I am currently interested in". In fact, we don't
     think you'll be referring to rows much and the whole
     thing should become fairly clear with a few examples.


     4:4. Logical expressions

     In the example above there is a condition which specifies
     which rows are to be included in the analysis, and in
     general a condition is a statement of a logical
     expression which is either true or false. So c5>6 is true
     for a given row if the value in the fifth column of that
     row is 9, but false if it is 2. Conditions are used to
     specify whether or not a row belongs to a given group or
     not, and in the example given whether or not it should be

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        Command syntax

     included with the other values towards deciding the
     sample mean, standard deviation, etc.

     b c1 if (c2-c3)<7

     means that if the statement given is true for a
     particular row then the value in column one will be taken
     and added to the sample and incorporated in the
     measurement of mean and standard deviation, but if not
     that particular row will be ignored for the purpose of
     the current analysis and left out of the sample.

     Here is a list of all the logical operators:

     x | y     x OR y     (either can be true)
     x & y     x AND y    (both must be true)
     x != y    x NOT EQUAL TO y
     x = y     x EQUAL TO y
     x < y     x LESS THAN y
     x > y     x GREATER THAN y
     x <= y    x LESS THAN OR EQUAL TO y
     x >= y    x GREATER THAN OR EQUAL TO y
     ! x       NOT x

     The expression is true if the relationship between x and
     y is as described, but false if not. The OR relationship
     is true if either condition x or condition y is true, and
     the AND relationship is true only if both condition x and
     condition y are true. (Note that the symbol for the OR
     operator, |, appears as a broken vertical line on most
     keyboards and is usually found on the same key as the
     backslash, \.) Here are some examples:

     c13>c12
     - the value in column 13 must be higher than the value in
     column 12

     c13<=c12
     - the value in column 13 must be less than or equal to
     the value in column 12

     !(c13>c12)
     - the value in column 13 must not be greater than the
     value in column 12, i.e. the same effect as the previous
     example

     c5>5
     - the value in column 5 must be greater than 5

     (c5>5)|(c6<10)
     - either the value in column 5 must be greater than 5 or
     the value in column 6 must be less than 10 for the
     condition to be true

     (c5>5)&(c6<10)
     - both the value in column 5 must be greater than 5 and
     the value in column 6 must be less than 10 for the
     condition to be true

     (c5>5)&(c5<10)
     - the value in column 5 must both be greater than 5 and
     less than 10, i.e. the value in column 5 must lie between

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        Command syntax

     5 and 10

     (c5=3)|(c5=5)|(c5=7)
     - the value in column 5 must be 3, 5 or 7

     (c5=3)&(c5=5)&(c5=7)
     - this can never be true, the value in column 5 cannot be
     3 and 5 and 7 all at once

     (c5!=3)&(c5!=5)&(c5!=7)
     - the value in column 5 must be anything except 3, 5 or 7

     (c5=2.2) | (((c5>5) & (c5<10)) & !((c5>6) & (c5<7)))
     - the value in column 5 can be 2.2, or else it must lie
     between 5 and 10 but must not lie between 6 and 7

     So you see expressions can be made as simple or as
     complicated as you like, and sub-clauses are contained in
     brackets. In fact the brackets are not always necessary -
     see the section below on operator precedence. Spaces
     occurring in logical and arithmetic expressions are
     ignored.

     When the keyword ROW is used in a condition then the
     number of the row itself is tested, so:

     row<5

     is true if the number of the row is less than 5, i.e. one
     of the first four rows.

     Contrast this to:

     c1<5

     which as we have already discussed means the rows for
     which the value in the first column is less than 5.

     There is no reason why references to rows and column
     cannot be combined in the same expression, e.g.:

     (c1<10) & (row<5)

     or even:

     c1<row

     Note to users familiar with spreadsheets:

     You will probably realise that these references to values
     are what are usually called relative references, they
     relate only to the column of the row in question. There
     is for example no direct way to compare values in an
     expression to the value in the third column of the fifth
     row - an absolute reference. A partial exception to this
     allowing references to the values in the first valid row
     only is described in the section on the ARITHMETIC
     command.





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        Command syntax

     4:5. Arithmetic expressions

     When we said C2-C3 in the first example, that was an
     arithmetic expression meaning (obviously) the value in
     column 2 minus the value in column 3. Many other
     operations are available, and here is a complete list:

     x + y     x MINUS y
     x + y     x PLUS y
     x mod y   x MODULO y
     x / y     x DIVIDED BY y
     x * y     x TIMES y
     x pow y   x TO THE yTH POWER
     x pX y   PROBABILITY OF CHI-SQUARED x WITH y DEGREES OF
                 FREEDOM
     x pT y    PROBABILITY OF STUDENT'S T x WITH y DEGREES OF
                 FREEDOM
     - x       NEGATIVE x
     abs x     ABSOLUTE VALUE OF x
     pN x      ONE-TAILED CUMULATIVE PROBABILITY OF x IN A NORMAL
                 DISTRIBUTION
     log x     LOG x BASE 10
     ln x      NATURAL LOG OF x (base e)
     exp x     e TO THE xTH POWER (natural antilog)
     lfact x   NATURAL LOG OF FACTORIAL x
     sin x     SIN x RADIANS
     arcsin x  ARCSIN x IN RADIANS
     cos x     COS x RADIANS
     arccos x  ARCCOS x IN RADIANS
     tan x     TAN x RADIANS
     arctan x  ARCTAN x IN RADIANS

     Arithmetic expressions can be written out just as they
     would appear on paper, again with brackets to clarify the
     order of operations:

      c3+c4*6
      (c3+c4)*6
      (c4*c5)pow3
      (c4*c5*c6)pow(1/3)

     The last example takes the geometric mean of columns 4,
     5, and 6. It multiplies them together and then takes the
     cube root of the product.

     c13 pX 3

     This example would take the value in column 13 to be a
     chi-squared statistic with three degrees of freedom and
     computes its probablility, or p value. See the section on
     the ARITHMETIC command for details of how to use EASISTAT
     as a set of statistics tables to look up.

     Numbers can be written for arithmetic expressions either
     as ordinary decimal numbers (37, -45.236, 11.4) or using
     exponential notation, where the mantissa is followed
     immediately by an E and the power of ten to multiply it
     by. Thus 3.3e5 is the same as 330000 and 2.7e-4 means
     0.00027. The results of the ARITHMETIC command are output
     in this format where appropriate.



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        Command syntax

     4:6. Operator precedence

     Operator precedence means the order in which logical or
     arithmetic operations are performed. We are all familiar
     with the idea that:

     3+4/2

     means three added to four-divided-by-two and not three-
     plus-four divided by two, so that the answer is 5 and not
     3.5.

     Here is a complete list of operator precedences:

      x pX y       x pT y
      x pow y
      x / y        x * y
      x - y        x + y
      x < y        x > y        x <= y        x >= y
      x != y       x = y
      x & y
      x | y

     The higher up an operator is, the sooner it is performed,
     as if it was enclosed in a pair of brackets. Operators in
     the same line are evaluated left to right, in the order
     in which they are read. This means that writing:

     c1+c2*c3+c4powc5*4pt15

     is equivalent to writing:

     c1 + (c2*c3) + ((c4powc5)*(4pt15))

     but that writing:

     c1-c2+c3

     is equivalent to writing:

     (c1-c2)+c3

     If you want the operations carried out in any other order
     then you have to explicitly specify it yourself using
     brackets.

     Note that you do not have to use brackets in the
     expression:

     (c5>5)&(c5<10)

     because:

     c5>5&c5<10

     will be interpreted in exactly the same way - the > and <
     take precedence over the &.






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        Command syntax

     4:7. Combining arithmetic
     and logical operations

     Not only can arithmetic and logical operations be
     arbitrarily complex, they can also be combined together
     in very flexible ways. Of course we have already seen
     examples of this because "(c2-c3)>7" combines an
     arithmetic expression, "c2-c3", with a logical one,
     "result>7".

     If this is the first time you are reading this manual
     then you may want to skip this section and come back to
     it later. Still here? Okay, here we go. The first point
     is that arithmetic values also have a logical value,
     which means that any number not equal to zero is
     logically true and any number equal to zero is false. So:

     1              is true
     0              is false
     4-3            is true
     3-4            is true
     3-3            is false
     3|1.5|0        is true
     3&1.5&0        is false

     The second, more useful, point is that any logical
     expression has an arithmetic value, which is 1 if it is
     true and 0 if it is false. So:

     3<4            = 1
     3>4            = 0
     (3<4)+(4<5)    = 2

     Which means we can write:

     c3*(c2<c3) + c2*(c2>=c3)

     to mean "whichever is higher of c2 and c3". If c3 is
     higher then the value inside the first brackets will be
     true, so 1. Then we multiply c3 by 1 and get c3. But the
     value in the second brackets will be false, or 0, and c2
     multiplied by 0 is 0 and the whole expression will
     evaluate to c3*1+0, or c3. If c2 is higher than c3 or
     equal to it then c2 will be given as the result.

     Here's another one:

     LN( C15*(C15>0) + 0.0001*(C15<=0) )

     The idea of this is to take the natural log of c15. But
     if c15 were less than or equal to zero then trying to
     take its log would cause an error, so what this
     expression in fact does is to take the natural log of c15
     if it greater than zero, but otherwise it takes the
     natural log of 0.0001.

     We hope this gives you an idea of the principles
     involved. You can do almost anything with the operators
     provided, though some things are a bit long-winded. More
     examples will be given in individual command
     descriptions, and especially in the descriptions of the
     ARITHMETIC, MACRO and INPUT commands.

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        Command syntax

     Incidentally, perhaps you can see now why we could not
     just write:

     5<c5<10

     to specify that c5 should lie between 5 and 10. EASISTAT
     would interpret the expression as follows: 5<c5 is either
     true or false; if it is true it has a value of 1 and if
     it is false it has a value of 0; whether it has a value
     of 0 or 1 it will still be less than 10, so the
     expression as a whole will always be true.


     4:8. General purpose
     variables

     As well as the values in the data table, EASISTAT
     provides a number of other variables which are not needed
     for the standard statistical tests but which may be used
     for a variety of other purposes and are particularly
     useful for general mathematical manipulations. Firstly,
     there are twenty general purpose variables which can be
     set to any values and used in arithmetic and logical
     expressions. These variables are referred to as V1,
     V2...V20, but they can also be labelled like the data
     columns and then referred to by these labels. The values
     are set by the DERIVE command and the labels are set by
     the LABEL command. For example if one wishes to have a
     value for pi available in expressions one could enter:

      LABEL V1 PI
      DERIVE PI ARCCOS(-1)

     This would set the label of first general purpose
     variable to be pi, and then set its value to be the
     arccos of -1 in radians. It could thereafter be referred
     to in expressions as pi, e.g.:

     C2+PI*C3

     These variables can be displayed with the command:

     LIST VARIABLES

     which can be shortened to:

     L V

     There are three special variables which are set by the
     BASICS command, and these are referred to as XNUMBER,
     XTOTAL and XMEAN. When the BASICS command is carried out,
     XNUMBER is set to the number of items present (valid rows
     used), XTOTAL is set to the total of the values used and
     XMEAN is set to the mean of the values (which would be
     XTOTAL/XNUMBER). The purpose of these variables is to
     make possible the construction of other statistical tests
     which may not be directly built in to EASISTAT. The
     values obtained from the BASICS command can be used in
     subsequent arithmetic expressions. An example of this is
     given in the section on the INPUT command.



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        Command syntax

     As an extension to this there are another twenty
     variables which are set by the BASICS command and other
     statistical commands. These are referred to as VV1,
     VV2...VV20. How these are set for each command can be
     discovered by displaying them after the command is
     performed. They are displayed by the command:

     LIST VV

     So if for example one wishes to use the value of the
     standard error of the mean as calculated by the BASICS
     command one could enter the following:

      BASICS C5
      LIST VV

     It then becomes clear that VV7 has been set to the
     standard error. If one wished to make a permanent copy of
     it one could then set one of the first twenty variables
     to have that value, since the value of VV7 itself will be
     changed by the next statistics command which is
     performed:

     DERIVE V1 VV7


     4:9. Rules for label names

     There are certain rules which must be followed for the
     labels used so that expressions will be parsed correctly.
     In general any combination of letters and digits can be
     used for the column titles and the labels of variables,
     but there are certain exceptions. Also note that there is
     no difference between upper and lower case letters, and
     that spaces in expressions are ignored.

     a) Don't start any label with a digit e.g. 1stname, 2A,
     etc.

     b) Don't start any label with a C or a V or a VV followed
     by a digit e.g. C2D, c40, v2, VV4xyz, etc.

     c) Don't call any column or variable ROW, P, G, E, RANKS,
     ZED, XNUMBER, XTOTAL or XMEAN.

     d) Don't start any label with the name of a mathematical
     function e.g. sint (uses SIN), pname (uses pN), etc. See
     the full list of arithmetic operators above.

     e) Don't start any label with the name of another column
     or variable, i.e. if one column is called DA, then no
     column or variable label must begin with the letters DA.
     (Strictly speaking this rule only applies to columns to
     the right of the first one, that is to say if that one
     column is titled DA then no column to the right of it
     should begin with DA.)

     If you get any problems with syntax errors or expressions
     not behaving as you think they should then come back and
     check these rules. For example if you did have a column
     called PNAME, then the expression sin(PNAME) would give
     you a syntax error with AME, because the parser would

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        Command syntax

     think that the PN referred to the normal probability
     function. Similarly if you had a column labelled 4 then
     the expression <4 would not mean "less than 4" but "less
     than the value in the column labelled 4".



























































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