gnuplot - Interpret character as sign -

I have some CSV data, which contains a letter data data which indicates the signal:

< Pre> ..., 123 h, ... ..., 200 h, ... ..., 150 s, ...

What is GNUPlot to H And is it possible to interpret S as positive and negative signal? In other words, the above data was plotted as

  ..., 123, ... ..., 200, ... ..., - 150, ... Gnuplot has a very limited ability to parse the string, however, your password should be  
 In case you can define a function that runs on the string values ​​of the respective columns and explains H and S: 
 
  v (s) = s [*: strlen 1: ( Using plot (2), plot 'file.txt' (S) -1] * (S [ST] Eln (s): - 1] Gathering 'S'? 1: 1)