ploticus: proc getdata

## proc getdata | Welcome Gallery Handbook |
| Manual page for proc_getdata(PL)

proc getdata accesses or defines data for plotting.`` proc getdata must be invoked before doing any plotting of data.`` The data which are read become the "current data set" that subsequent plotting procs will access, and replace any data that were read in (or generated) previously.``

## Features

- Data may be specified literally within the script file, or it may be located in an external file or be the result of an externally executed command, or perhaps even an SQL command.``
- Conditional selection of data records (`select`).``
- Data filtering (`filter`) for purposes such as combining or rearranging fields, performing calculations, truncating outliers, etc.``
- Field names may be assigned explicitly (`fieldnames` or `fieldnamerows`), or via a data file header line (`fieldnameheader`). These names can then be used anywhere a data field reference is expected.``
- Data sets with variable number of fields per row can be accomodated by setting a maximum `nfields` value.
- Data may be located at the end of the script file, to get it out of the way (`#intrailer`).``

## Examples

Virtually all of the Gallery examples use #proc getdata.``

## Acceptable data formats

See dataformat .``

## Prerequisites

None.``

## Troubleshooting

Set `showresults: yes` in order to see the data after it is read and parsed.`` Especially useful when working with `filter`.``

## Variables that are set

The variable NRECORDS will be set to the number of records read, and the variable NFIELDS will be set to the number of fields per record.``

## Handling error conditions gracefully

If no data records were read, NRECORDS will be set to zero.`` This may be tested using script code such as this, which generates an image containing the words "No data found" :

       #proc getdata
          ...

       #proc endproc
       #if @NRECORDS = 0
         #proc annotate
         location: 3 3
         text: No data found.

         #exit
       #endif

## Setting variables from within a data file

Data files may contain embedded #set commands to set ploticus variables.`` This may be a convenient way for title, labels, etc. to be driven by the data file.`` The syntax is the same as in ploticus scripts:

  `#set` varname`=` value

varname will be set to value. value may contain embedded spaces or any other character. value may not be a $function(), nor may it contain any other @variables.`` None of the other script operators, such as #if, are supported in this context.``

## Mandatory attributes

One (and only one) data source (either `file`, `pathname`, `command`, `data`, or `sql`) must be specified.`` Default field delimitation method is `spacequoted`; `delim` must be set for other types such as tab-delimited or comma-quote delimited.``

## Attributes

data multiline-text

  Literal specification of plotting data. Terminates at first blank (empty) line. Data may include a field name header.`` Example:

      data:   "Case 1"   0   4   4.1
              "Case 2"   1   5   4.4
              "Case 3"   2   2   4.0
              "Case 4"   3   9   4.8

  ``You can also capture data from a shell command this way (this allows you to use multi-line shell commands) for example:

         #proc getdata
           data:
            #shell
               shell command
            #endshell

  The `#sql` command can be used similarly, in builds that support it.``

file filename

  Shell-expandable name of a file containing plotting data.`` This name will be used along with cat(1) in a shell command, thus exported shell variables and metacharacters may be part of the name.`` A dash (-) may be used if data is to be read from the standard input, (or the `standardinput` attribute may be used).`` Example: `filename: myfile.dat`

pathname filename

  Name of a file containing plotting data.`` The file will be opened directly.`` Shell variables and metacharacters may not be used.``

command shell command line

  An external shell command that will produce plot data on its standard output.``
  Example: `command: cat mydat | uniq -c`

sql sql command

  In ploticus builds that support it, invoke the given SQL command, and capture the results directly. Result column names become the ploticus field names (to handle join result column names that contain embedded periods (.), you can use #control dot_in_varnames ). `delim`, `fieldnames` (etc.), `select` and `filter` have no meaning in this mode.

delim `spacequoted` | `whitespace` | `comma` | `tab`

  The type of delimiting method to be used when parsing the data. `spacequoted` is the default (`space` is equivalent to `spacequoted`). See dataformat for details.``
  Example: `delim: comma`

fieldnames namelist

  If specified, the names given in namelist may be used in any plotting proc to identify data fields. namelist is a list delimited by spaces and/or commas.`` Names may include any alphanumeric characters with a maximum length of 38, and are case-insensitive.`` Field names may not contain embedded spaces or commas.``
  Example: `fieldnames: date group n`

fieldnamerows multiline text

  Same as `fieldnames` (see above), except that field names are given one per line.`` Must be terminated by a blank line.`` Example:

      fieldnamerows:
        id
        type
        age
        sex

fieldnameheader `yes` | `no`

  Allows field names to be embedded in the input data.`` If `yes`, the first non-comment line in the data is expected to contain field names. This line is not considered part of the data.`` The field name header should be delimited like the rest of the data.`` Field names may not contain embedded white space, commas, or quote characters.``

pf_fieldnames namelist

  Post-filter fieldnames, for use with `filter` when field names are being used, and the filter result has a different logical record format than the input.``
  Example: `pf_fieldnames: date z sum1 sum2`

nfields n

  If specified, this sets the expected number of fields per record.`` If a data row has more than the expected number of fields, extra fields are silently ignored. If a data row has less than the expected number of fields, blank fields are silently added.`` This is applied after any `filter` processing.``

standardinput `yes` | `no`

  If `yes`, data is read from the standard input.``

#intrailer

  Indicates that a `data` attribute will be given in a #proc trailer, at the end of the script file.`` See EXAMPLES, below.``

commentchar string

  A character or group of characters that is used to signify a comment in the data file.`` Commented lines will be skipped. Default is `//`.`` Example: `commentchar: #`

showresults `yes` | `no`

  If `yes`, the results, after any selecting and/or filtering, are written to the diagnostic file, which may be useful in debugging, etc.``

rotate `yes` | `no`

  Allows data to be given all in one row, even when plotting proc expects one record per instance (which most do).`` Only applicable if your data set has one row.`` (There still must be a blank line following the data attribute.) To rotate more than one row, use proc processdata.``
  Example: see bars1

select conditional expression

  This allows data records to be selected for inclusion based upon a selection expression. Incoming data fields are referenced by number, using a double at-sign (`@@`) prefix. Hint: use the `showresults` attribute when debugging.``
  Example: `select: @@3 = g`
  This would select all data records having 3rd field equal to `g`.``

filter multiline text

  An embedded script which allows flexible processing to be applied to incoming data records one at a time.`` Typical uses are for concatenating or splitting fields, doing on-the-fly date conversions, or generating derived fields such as the sum of several fields or the difference between two fields.``
  The embedded script will be applied once to every incoming data record.`` The script should produce some "output"; generally the last statement is a ##print. The output must use the same delimitation method as the input.`` The output may have a different logical record format than the input.`` If you are using field names, the `pf_fieldnames` attribute (see above) may be used to name the filter result fields when result record format differs from that of the input.``
  The script uses the same syntax as the greater ploticus script, except that:

  - directives must begin with two pound signs (`##`) instead of one
  - local variables begin with two at signs (`@@`) instead of one
  - fields on the incoming data record are accessed like this: `@@1` for the first field, `@@2` for the second, etc. If you are using field names, these may be used as well, eg: `@@score`.``
  - the only directives that may be used are ##set, ##if, ##elseif, ##else, ##print, ##call, and ##exit

  Other things worth noting:

  - the filter script is terminated using a blank line.``
  - use the `showresults` attribute when debugging.``
  - if `filter` is used along with select, the `select` is applied first.
  - `filter` cannot be used on data specified using the `data` attribute.``
  - `filter` can only access fields from one data record at a time.``
  - variables from the ploticus script may be referenced within the `filter` script (use one at-sign `@`).`` Evaluation occurs before the filter script executes.``
  - ploticus script #if/#else statements (single pound sign) may be used to selectively execute portions of the filter script.`` Interpretation occurs before the filter script executes.``
  - Example: This filters out data records having field 2 or field 3 equal to M. It then calulates the difference in days between two dates and puts this difference in the variable DIFF.`` Finally it "prints" incoming field 1 along with DIFF.`` Thus the result of this #proc getdata will have be data records having two fields.``

         filter:
              ##if @@2 = M || @@3 = M
                ##exit
              ##endif
              ##set DIFF = $daysdiff(@@3,@@2)
              ##print @@1 @@DIFF

    ``
  - There are several more `filter` examples in the FAQ

## More examples

Data specification may be located at the end of the script file by using #intrailer and #proc trailer. This may be useful in "getting the data out of the way", or with automated building of script files.`` Here is how this is done:

     #proc getdata
     #intrailer

    other #procs, etc.

     #proc trailer
     Data:	0.3 0.5 2.3
    	3.5 9.4 1.4
    	..etc..
    end of file

    data display engine

    Copyright Steve Grubb

Markup created by unroff 1.0, `` `` December 10, 2002.