2.12.1.5 index

The index keyword allows you to select specific data sets in a multi-data-set file for plotting.

Syntax:

      plot 'file' index <m>{{:<n>}:<p>}

Data sets are separated by pairs of blank records. `index <m>` selects only set <m>; `index <m>:<n>` selects sets in the range <m> to <n>; and `index <m>:<n>:<p>` selects indices <m>, <m>+<p>, <m>+2<p>, etc., but stopping at <n>. Following C indexing, the index 0 is assigned to the first data set in the file. Specifying too large an index results in an error message. If index is not specified, all sets are plotted as a single data set.

Example:

      plot 'file' index 4:5

For each point in the file, the index value of the data set it appears in is available via the pseudo-column `column(-2)`. This leads to an alternative way of distinguishing individual data sets within a file as shown below. This is more awkward that the index command if all you are doing is selecting one data set for plotting, but is very useful if you want to assign different properties to each data set. See `lc variable`.

Example:

      plot 'file' using 1:(column(-2)==4 ? $2 : NaN)        # very awkward
      plot 'file' using 1:2:(column(-2)) linecolor variable # very useful!

splot with indices demo.