Formatting

The default way in which APL displays results may not always suit your requirements. Obviously you can do a certain amount by using functions like size to reshape data, or catenate to join data items, but for many applications you may want much more sophisticated facilities. You may, for example, want to insert currency signs and spaces in numeric output, or produce a neatly formatted financial report, or specify precisely the format in which numbers are displayed.

APLX has a variety of functions for formatting data, providing flexibility as well as compatibility with a number of other APL interpreters.

Formatting functions

There are three functions in APLX which all convert the format of data from numbers to characters, and allow you to specify how the converted numeric data should be laid out.

The functions are:

• The ⍕ primitive (Format, Format by specification, Format by example)
• The ⍺ primitive (Picture format)
• The ⎕FMT system function.

Each function lets you specify how many character positions a number should occupy when it is displayed, and how many of these positions are available for decimal places. The number of characters and number of decimal places are specified in the left argument:

      6 2 ⍕ 1341.82921
341.83

(Note that since the number had to be truncated to fit the character positions allowed, it was first rounded to make the truncated representation as accurate as possible.)

Picture format (⍺) and Format by Specification (⍕ with a character left argument) allow you to use editing characters to define a 'picture' of how data should look when it is displayed. The picture is the left argument and the data the right.

The following example shows the values in a 4-row 2-column matrix called TAB. It then shows the ⍺ function applied to this matrix and its effect on TAB:

      TAB
1096.2   ¯416.556
 296.974 1085.238
¯811.188  844.074
¯745.416  153.468
      '$$Z,ZZ9.99 DR       ' ⍺ TAB
 $1,096.20               $416.56 DR
   $296.97             $1,085.24
   $811.19 DR            $844.07
   $745.42 DR            $153.47

⎕FMT takes the process a stage further, allowing a variety of picture phrases, qualifiers and decorators to be supplied as the format specification.

      'B K2 G< ZZ9 DOLLARS AND 99 CENTS>' ⎕FMT 8.23 12.86 0 2.52
   8 DOLLARS AND 23 CENTS
  12 DOLLARS AND 86 CENTS

   2 DOLLARS AND 52 CENTS