gnuplot, how to label only certain points?

Question

I'm using the following gnuplot commands to create a plot:

#!/bin/bash
gnuplot << 'EOF'
set term postscript portrait color enhanced
set output 'out.ps'

plot 'data_file' u 3:2 w points , '' u 3:2:($4!=-3.60 ? $1:'aaa') w labels

EOF

where data_file looks like this:

  O4     -1.20     -0.33     -5.20  
O9.5     -1.10     -0.30     -3.60  
  B0     -1.08     -0.30     -3.25  
B0.5     -1.00     -0.28     -2.60  
B1.5     -0.90     -0.25     -2.10  
B2.5     -0.80     -0.22     -1.50  
  B3     -0.69     -0.20     -1.10  

I want gnuplot to label all points with the strings found in column 1, except the one where column 4 is equal to -3.60 in which case I want the aaa string. What I'm getting is that the $4=-3.60 data point is being labeled correctly as aaa, but the rest are not being labeled at all.

---

Update: gnuplot has no problem showing numbers as labels using the conditional statement, ie: any column but 1 is correctly displayed as a label for each point respecting the conditions imposed. That is, this line displays column 2 (numbres) as point labels respecting the conditional statement:

plot 'data_file' u 3:2 w points , '' u 3:2:($4!=-3.60 ? $2:'aaa') w labels

Update 2: It also has no problem in plotting column 1 as point labels if I plot it as a whole, ie not using a conditional statement. That is, this line plots correctly all the point labels in column 1 (strings):

plot 'data_file' u 3:2 w points , '' u 3:2:1 w labels

---

So clearly the problem is in using the conditional statement together with the strings column. Any of these used separately works just fine.

Answer 1

In a more clean way maybe, this should work. It seems label can't display a computed number if it isn't turned in a string.

#!/bin/bash
gnuplot << 'EOF'
set term postscript portrait color enhanced
set output 'out.ps'

plot 'data_file' u 3:2 w points , '' u 3:2:($4!=-3.60 ? sprintf("%d",$1):'aaa') w labels

EOF

Answer 2

Is this what you want?

#!/bin/bash

gnuplot << 'EOF'
set term postscript portrait color enhanced
set output 'out.ps'
plot 'data_file' u 3:2 w points , \
     '' u (($4 == -3.60)? 1/0 : $3):2:1 w labels

EOF

All I do here is set (x) points where the column 4 equals -3.6 to NaN (1/0). Since gnuplot ignores those points, life is good. I think the problem with your script is that you were filtering a column where gnuplot expects string input -- although I haven't played around with it enough to verify that. I just switched the filter to a column where gnuplot expects numbers (the x position) and it works just fine.