#494 real numbers in for loop iterator

[cipper]

Presently only integers are accepted in 'for' iterator, while often real numbers are needed, es.:
p for [i = 0.1 : 1.0 : 0.1] "mydata".i

Such generalization would be very appreciated.

[cipper]

any feedback?

[Ethan Merritt]

There has been discussion about this before. I don't think a solid case has been made that it gains enough to be worth the added complexity. The example you give wouldn't actually work anyway because autopromotion of a floating point value to a string is not well defined. And as soon as you bring a format into it, you might as well use the integer equivalent:

plot for [i=1:10] sprintf("mydata.%.1f", i/10.)

[cipper]

The promotion to string can always be done by "".i
i.e. by concatenating with an empty string.

Your sprintf() solution is indeed a workaround, but it could actually make the script quite more complex and messy than it should be. Take for example an apparently simple case like:

p for [i = 8.562 : 12.137 : 0.065] "data_".i

This format would be clear and straight, and does not require one to work it around by something like:

end=int((12.137-8.562)/0.065)
plot for [i=0:end] sprintf("data_%.3f", 8.562+i*0.065)

which is a quite unreadable way to get a simple iteration.

[Ethan Merritt]

You are missing the point. What string is produced by

foo = 1./3.
filename = "data_".foo

"data_.3" ? "data_0.3"? "data_0.333333333333333333"?

Without a format specifier the result of the automatic conversion is undefined.

[cipper]

You are right. I thought that the "".i trick worked also for floats...

[cipper]

rather, one could use the system() call (as you teach):

p for [i in system("seq 8.562 0.065 12.137")] (i+0) t i

which is clean enough. However, if it wasn't a big change, the direct iteration (without workarounds) would be best. There's really so much to change to get this?

Thank you,
Roberto

[Ethan Merritt]

No need to jump outside gnuplot and invoke the system shell.
There are multiple ways on doing this in gnuplot itself:

array FOO = [ 8.562, 0.065, 12.137]

do for [i=1:|FOO|] {
      ... something using FOO[i]
 }

 BAZ = "8.562 0.065 12.137"
 do for [i=1:words(BAZ)] {
    ... something using word(BAZ,i)
 }

[cipper]

What you write is totally different from my case. You are just iterating among the 3 elements of an array, not among 55 elements of a sequence from 8.562 to 12.13 in steps of 0.065, as I would get from the system() call above.

[Ethan Merritt]

Ah, sorry. I was not familiar with the "seq" command so I misinterpreted your example.