The World of Computer Software/World_Of_Computer_Software-02-385-Vol-1of3.iso/e/estat21.zip/EASIDOC.ZIP/ESCHAP10.DOC

Text File | 1992-06-30 | 18KB | 397 lines

     Chapter 10: RUNNING EASIGRAF

     EASIGRAF reads in data from text files called graph
     files. These consist of a series of values arranged in
     rows and columns and some other information about the
     type of graph to be drawn, the graph titles, etc. The
     format of these files is explained more fully in the
     chapter entitled "Format of graph files", but if you are
     using EASIGRAF with EASISTAT then you do not have to
     worry much about them because EASISTAT prepares files in
     the correct format automatically. The program is
     specially designed so that graphs can be displayed by
     EASISTAT just by specifying a "G" option on some of the
     commands.

     EASIGRAF can organise the data read in from the file in
     different ways - values can be grouped according to rows,
     columns, rows and columns, or pairs of columns can be
     plotted against each other. Vertical bar charts, line
     graphs and scatter plots can be drawn, and there are
     options to alter scaling, shading and other aspects of
     the display. Titles may be added, deleted or changed.
     There is also some capability to produce 3D graphs.

     The modified graph can be saved to disk as a graph file
     so that the next time it is displayed it will be shown in
     its updated form. The graph can also be saved to disk as
     a binary screendump called a Microsoft Paint file or MSP
     file for short. In this form it can be printed out to a
     printer using the PRMSP program. An important feature is
     that if you have the Microsoft Windows program you can
     use Microsoft Paint to read in the MSP file and make
     further adjustments to the graph image before eventually
     printing it out.

     EASIGRAF is designed to use a similar format of graph
     file to the graphing program called PCG2 which is
     supplied with the Shareware database PC-File. This means
     that for some kinds of graph you can use PCG2 instead of
     EASIGRAF. The advantages of PCG2 are that it can produce
     pie charts and it can generate PostScript output.
     Unfortunately it does not plot Y values against X values
     and it does not handle missing values in the same way as
     EASIGRAF.

     EASIGRAF can display graph files from any source provided
     they are in the correct format. They may be produced by
     EASISTAT or PC-File, or they can be typed out by hand
     using the EDIT program or another ASCII text editor. One
     thing that is often particularly useful is to use an
     editor to make adjustments to graph files, for example to
     change titles and the like, after they have been produced
     by EASISTAT. Using EASIGRAF itself to alter titles is
     possible but can be rather slow and awkward.

     To display a graph file with EASIGRAF type:

     EASIGRAF [filename]

     If no file name is given then the name GRAPH.ME is used
     (so typing EASIGRAF on its own if there is no file called
     GRAPH.ME present in the directory will produce an error

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     message saying that GRAPH.ME could not be found).

     If the graph file is read in successfully then it will be
     displayed in its default format and the main menu will be
     shown. The following options are available:


     10:1. Main menu

     The main menu is displayed which shows the commands
     available by pressing a variety of keys detailed below.
     Pressing M hides the main menu. To see it again press M
     again.


     10:2. Scatter chart

     This is selected by pressing the S key. Each pair of X
     and Y values is plotted as a point. It is possible to
     change the symbols used to display the points by using
     the shading option from the KEY menu.


     10:3. Line graph

     This is selected by pressing the L key. Each pair of X
     and Y values is plotted as a point and lines are drawn
     between them. It is possible to change the type of line
     used by using the shading option from the "Key" menu.
     Breaks in the lines can be produced by using the keyword
     OMIT in the data of the graph file.


     10:4. Vertical bar chart

     This is selected by pressing the V key. Each pair of X
     and Y values is plotted as a vertical bar. The default
     width for these bars is 1, but this can be changed
     setting a constant value for the Z axis (see the section
     on the "Data" menu). Alternatively variable width bars
     can be produced by using values from a third data column
     to provide the widths required. It is possible to change
     the shading of the bars by using the shading option from
     the "Key" menu. The bars can be displayed as solid blocks
     if the 3 key is pressed (see below).


     10:5. Three dimensions

     This option is turned on and off by pressing the 3 key.
     The Z axis of the graph is not displayed but goes off
     towards the top right corner of the screen. For line and
     scatter charts points will be plotted in this dimension
     also according to the value of the Z coordinate. A
     vertical line is also drawn from the Y=0 plane to each
     point to give a better impression of the height. For bar
     charts "blocks" are drawn instead of "bars". Note that
     plotting points in 3 dimensions does not affect the
     autoscaling which EASIGRAF performs. Because this
     autoscaling depends only on the X and Y values and not
     the Z values, this means that points may tend to go off
     the top of the screen. In such a situation the X and Y

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     scales have to be adjusted manually (by using the "Axes"
     menu) to get the graph to the right proportions. If
     three-dimensional plots are required the column for Z
     coordinates will usually have to be selected explicitly
     by using the "Data" menu, as in most cases the default Z
     coordinate is a constant.


     10:6. Axes menu

     This is selected by pressing the A key. The X and Y axis
     can be toggled on or off, as can the ticks and numerical
     values showing the scale along the axes. The whole graph
     can be rescaled by changing the maximum and minimum
     values for X and Y, and the increment or distance between
     ticks can also be altered. Enter three values for
     minimum, maximum and increment separated by two commas.
     None of the changes made will take effect until you leave
     the "Axes" menu by pressing ENTER, at which point the
     graph will be redrawn with the new values.


     10:7. Titles menu

     This is selected by pressing the T key. It allows all the
     different titles to be turned on or off or edited. Which
     titles appear where depends on the way the data is
     organised as selected from the "Data" menu. For any
     particular grouping this can be discovered by a bit of
     trial and error, and by comparing how graphs appear on
     the screen compared with the contents of the graph files.
     An added complication is that the way some of the titles
     are used depends not only on the type of graph as
     selected from the "Data" menu, but also on whether there
     are one or more groups of data to refer to. For example
     EASIGRAF attempts to select the most suitable title for
     the Y axis according to circumstance. If one column
     provides the Y variables for a graph then the title of
     that column will be used, but if more than one column
     provides Y variables the vertical title (TITLEV) from the
     graph file will be used instead. Similar considerations
     apply to the X axis titles when there are one or more
     than one groups of frequency data to display.

     Special "floating" titles can also be added to the graph
     - these can be made to appear anywhere on the screen and
     can read left to right, upwards, downwards or upside
     down. To produce a floating title first type in the
     message that you wish to have appear and press ENTER and
     then type in the coordinates and angle for it, separated
     by commas. The graph on the screen occupies the region
     from coordinates 0,0 to 1,0.6 and the floating title can
     begin anywhere within this region or within a border 0.1
     units wide around it. So the first value for the position
     must be between -0.1 and 1.1 and the second value must be
     between -0.1 and 0.7 (these values are completely
     independent of the graph scale, the title should always
     appear in the same position on the screen). The values
     for the rotation are in degrees anti-clockwise from the
     usual left to right. If the rotation is omitted it will
     be taken as zero. So legitimate values to input would be
     "0,0.3,90" or "0.7,-0.05,180" or "-.1,.1".

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     10:8. Regression menu

     This is selected by pressing the R key. It allows the
     mean Y value and regression lines to be toggled on and
     off. In some types of graph the regression lines would be
     meaningless and so they are drawn in the same place as
     the mean. "Y on X" means "the regression of the Y
     variable on the X variable".


     10:9. Exchange data

     This is selected by pressing the X key. This exchanges
     the data plotted in various ways. If the data points were
     grouped by columns they will now be grouped by rows and
     vice versa. If they were grouped into rows and then
     columns they will now be grouped into columns and then
     rows. If pairs of columns were plotted against each other
     as X and Y variables they will be swapped over. Note that
     using this option causes automatic rescaling of the axes.


     10:10. Data menu

     This is selected by pressing the D key. It determines how
     the data in the graph file is organised and extracted for
     graphical representation. Different options are more
     suitable for different types of data, and in many cases
     choosing a different organisation of the data will
     produce nonsensical results. Again, a little trial and
     error will be harmless and instructive, and it is also
     helpful to study the files used for the demonstrations.
     The graph is redrawn when leaving this menu, and
     automatic rescaling of the graph is always performed.

     10:10.1 Group by rows and columns

     This is most appropriate when the data values consist of
     frequency data from a contingency table to be plotted as
     a histogram. The row and column are combined to provide
     the X coordinate for a point and the data value provides
     the Y coordinate. The points are grouped according to the
     row in the graph file. X axis titles for the groups of
     points are provided by the row titles and the main X
     title is provided by the overall row title (TITLEC). The
     points are shaded differently according to the column in
     the graph file and a key is provided linking this shading
     with the column titles. Regression lines and means are
     available for each group of points (i.e. all those from
     the same row). An example of this kind of graph file is
     HISTO.GRP, and this is the type of graph used by the
     CHISQ command of EASISTAT to produce frequency
     histograms.

     10:10.2 Group by columns and rows

     This option is the corollary of the above with the rows
     and columns of the graph file exchanged. The points would
     be grouped by columns and the shading and key would
     indicate the row, with the column and row titles being
     used appropriately. You can exchange between this
     arrangement and the previous one by pressing the X key.

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     10:10.3 Group by rows

     The X coordinate of a point is provided by the row which
     the data value appears in, and the Y coordinate is
     provided by the value itelf. All values in the same row
     will appear in the same vertical line. It is the
     corollary of the the next option, which is more generally
     useful.

     10:10.4 Group by columns

     The X coordinate of a point is provided by the column
     which the data value appears in, and the Y coordinate is
     provided by the value itelf. All values in the same
     column will appear in the same vertical line. The X axis
     titles are provided by the column titles and a main X
     title is provided by the overall column title (the first
     TITLEG). The Y axis title is provided by the vertical
     title (TITLEV). This kind of graph is really only clear
     when displayed as a scatter chart (selected by pressing
     S). It is very useful for displaying the values of
     different groups of measurements, and is used in this way
     by the ANOVA command of EASISTAT. The means of the groups
     can be displayed, but the regression lines would be
     meaningless and so are displayed in the same place as the
     mean. An example of this kind of graph file is ANOVA.GRP.
     You can exchange between this arrangement and the
     previous one by pressing the X key.

     10:10.5 XY columns

     Columns of values are taken in pairs and plotted against
     each other, the first column providing the X coordinate
     and the second the Y coordinate. An indefinite number of
     pairs of columns may be specified, and all will be
     plotted simultaneously. Each pair of columns is shaded
     differently and if there is more than one pair an
     appropriate key is provided. If there is only one pair of
     columns then the titles for the X and Y axes are provided
     by the titles of these columns. If there is more than one
     pair then the Y axis title is provided by the vertical
     title (TITLEV) and the X axis title is provided by the
     overall group title (the first TITLEG).

     For each pair an optional third column can be specified
     (the "Z value"). This third column determines the width
     of the bars in a bar chart, allowing variable width bars
     to be created. For scatter and line graphs it determines
     the distance that a point is displaced towards the top
     right of screen when the "three dimensions" option is
     selected. If no third column is specified then all the Z
     values will be equal to the default which is 1. If a
     negative number is given as the third value then this is
     taken to represent a constant rather than a column
     number. The absolute value of this constant is the Z
     coordinate for all the data points, so for example
     entering 2,3,-0.5 would plot column three against column
     two and all the columns would have a Z value of 0.5. The
     most useful application of this is to produce bar charts
     with bars of width other than 1. There is no way to
     assign a negative constant Z value.


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     10:11. Key menu

     This is selected by pressing the K key. It allows the key
     to be toggled on or off or moved to a new position. It
     also allows the shading of the graph to be altered. There
     are five positions for the key: top-left, top-right,
     bottom-left, bottom-right and centre. They are numbered
     from one to five in that order. Different numbers for the
     shading produce different types of point, line and bar.
     These are best discovered by trial and error. Selecting a
     number other than zero causes all points to be displayed
     according to that number. Selecting zero (the default)
     allows points associated with different variables to be
     displayed differently. However there is no way to
     explicitly assign different shadings to different
     variables apart from this default scheme. For graphs for
     which no key is appropriate, a box appears with the
     message "No key". This can be turned off by toggling the
     key. No changes made will take effect until you leave the
     "Key" menu by pressing ENTER, at which point the graph
     will be redrawn with the new values.


     10:12. Files menu

     This is selected by pressing the F key. It allows the
     graph to be saved either as a graph file or as a
     Microsoft Paint (MSP) file. If it is saved as a graph
     file then all the information required to redisplay it
     almost exactly as it appears on the screen will be saved,
     such as the current scale and title and axis
     configurations.

     The graph must be saved as a Microsoft Paint file before
     it can be printed out. Doing this also means that if you
     have Microsoft Windows and Paint then you can edit the
     graph by hand to produce a more polished product. The
     newest versions of Windows Paint expects the file to be
     in a format called BMP instead of MSP, but the MSP files
     can still be read in provided the option to do this is
     selected when using Paint.


     10:13. Quit

     This is selected by pressing the Q key and quits
     EASIGRAF. Be sure to write any MSP files that you want
     and save any changes to the graph file first.



     Note that when you select an option from the menu and
     then make changes, sometimes these changes will not be
     apparent until you return from the option to the main
     menu. It is at this point that the graph is redrawn. For
     example if you wish to turn off the key you would type
     "K1" to toggle the key. Nothing appears to happen.
     However when you leave the "Key" menu by pressing ENTER
     the graph is redrawn, this time without the key. This
     sort of thing applies in several other situations.



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