gnuplot: check if vector or column/row of *.dat are zeros?

in gnuplot, I need to find out if a whole column of my data file is zeros (maybe by summoning up the elements?). How do I address this column outside of "using 1:2 .."? is there a short way to check this or is the sum neccessary (and how would I do that, I just found a way to add columns in a plot, but not the column itself)? I'd like to write something like if(data(:,1)==zeros) ... or: if(sum(data(:,1))==0) ...