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(gnuplot.info)Ternary

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 There is a single ternary operator:

     Symbol       Example      Explanation
       ?:          a?b:c     ternary operation

 The ternary operator behaves as it does in C.  The first argument (a), which
 must be an integer, is evaluated.  If it is true (non-zero), the second
 argument (b) is evaluated and returned; otherwise the third argument (c) is
 evaluated and returned.

 The ternary operator is very useful both in constructing piecewise functions
 and in plotting points only when certain conditions are met.

 Examples:

 Plot a function that is to equal sin(x) for 0 <= x < 1, 1/x for 1 <= x < 2,
 and undefined elsewhere:
       f(x) = 0<=x && x<1 ? sin(x) : 1<=x && x<2 ? 1/x : 1/0
       plot f(x)
 Note that `gnuplot` (Note: gnuplot ) quietly ignores undefined values, so
 the final branch of the function (1/0) will produce no plottable points.  Note
 also that f(x) will be plotted as a continuous function across the
 discontinuity if a line style is used.  To plot it discontinuously, create
 separate functions for the two pieces.  (Parametric functions are also useful
 for this purpose.)

 For data in a file, plot the average of the data in columns 2 and 3 against
 the datum in column 1, but only if the datum in column 4 is non-negative:

       plot 'file' using 1:( $4<0 ? 1/0 : ($2+$3)/2 )

 Please see `plot data-file using` (Note: using ) for an explanation of the
 using syntax.