How gnuplot convert a string to integer
I wonder if there is an easy way to convert a string to integer. For example, I want a way as like strtointeger("2") to return an integer 2.
columns="2 3"
plot for [i in columns] "mydata.dat" using 1:strtointeger(i)
The variable i in [i in columns] is actually a string. So, convert it to an integer via int(i).
If you want to plot a column defined by an integer variable, use ... using (column(i))....
So, in combination:
Code:
### plot column numbers from a sequence in a string
reset session
set key top left
$Data <<EOD
11 12 13 14 15
21 22 23 24 25
31 32 33 34 35
41 42 43 44 45
51 52 53 54 55
EOD
columns="2 3 5 1 4"
plot for [i in columns] $Data using 1:(column(int(i))) w lp title sprintf("Column %s",i)
### end of code
In your case remove the datablock $Data <<EOD ... EOD and in the plot command replace $Data with "mydata.dat"
Result:
using 1:(int(i)) rather than using (column(int(i))). I mean the function column must be used with parentheses, but parentheses used with int is a wrong use, why?
(int(i)) it will be a constant with value i. Whereas (column(i)) are the values from the ith column.real type. Really thanks to your answer, which let me know that string type can also be used with int!int(1.23), int("1.23") and even int("1.23abc") will work, whereas int(abc1.23) or int("abc1.23") will give error messages.using 1:int(i) would also give the same desired result like using (column(int(i))), in contrast to using 1:(int(i)), (note the additional parentheses).