gnuplot: how to know the last column number? - gnuplot

Question

I have a problem handling data using gnuplot.
My data has different column number per line.
I want to plot with X-axis of the first column and Y-axis of the last.
The last columns are always different every line.
For example, my data looks like that (my.dat)
1 2
2 1 3
3 4 4
4 5
5 2 1 3 6
plot 'my.dat' us 1:(lastcolumn) w l
Before reading in gnuplot, I can pre-process of the data.
But my gnuplot is windows version, I cannot use awk or any parsing program.
So I hope it handles only into gnuplot.
Is that possible?
Thanks

Answer 1

Yes, you can check that with gnuplot. The idea is as follows:
You analyze your data with stats and inside the using you check recursively with valid which column is the last valid. If an invalid column is reached you return the number of the previous column otherwise the next column is checked. The last column is then contained in the variable STATS_max
check_valid_column(c) = valid(c) ? check_valid_column(c + 1) : c - 1
stats 'my.dat' using (check_valid_column(1)) nooutput
last_column = int(STATS_max)
plot 'my.dat' using 1:last_column

Answer 2

Just for the records, here is an alternative suggestion. Christoph's solution is certainly more elegant and probably faster.
However, with the recursive approach you will get an error "recursion depth limit exceeded" if you have more than 250 columns (admittedly, probably very rare cases).
The solution below uses the lines as one string and counts the columns with words(). This, however, works only if you have whitespace as separator. With comma it will not work. Not sure what string length limit would be.
Code: (edit: no need to plot to a dummy table, stats can be used instead)
### find the maximum number of columns
reset session
# create some random test data
set print $Data
rows = int(rand(0)*5+5) # random 5 to 9 lines
do for [r=1:rows] {
minCols = 251 # if minCols >250, the recursive approach will fail
cols = int(rand(0)*10+minCols)
line = ''
do for [c=1:cols] { line = sprintf("%s %d",line,rand(0)*10) }
print line
}
set print
# alternative approach with word(). Works only for separator whitespace.
set datafile separator "\n"
maxCol=0
stats $Data u (cols=words(strcol(1)), cols>maxCol?maxCol=cols:0) nooutput
set datafile separator whitespace
print "words() approach: ", maxCol
# Recursive approach for comparison
print "Recursive approach: "
check_valid_column(c) = valid(c) ? check_valid_column(c + 1) : c - 1
stats $Data u (check_valid_column(1)) nooutput
last_column = int(STATS_max)
print last_column
### end of code
Result: (if number of max columns>250)
words() approach: 259
Recursive approach:
"SO41032862.gp" line 28: recursion depth limit exceeded