[Janos Torok]

Old and bad code, works only for linux but our group
uses it a lot. I hope someone rewrites it and includes
it in the distribution.

The purpose of this script is to facilitate the
command line plotting of many files with numerous
columns. (A general problem in science.)

Works for commands: plot, splot and replot

If filename contains * or ? the filename is passed to
the shell echo command to complete it. All returned
files are then plotted with the same arguments. Note
that shall also extends other wildcards like `[a-z]'
and naturally it can be used but in order to pass it
to the shell the filename must contain a star or a
question mark.

If the using field contains the `@' character and
numbers before and after (e.g. using 1:2@6) than the
plotting is modified and the plotting is executed with
all number between the given limits. For example:
> plot "a.dat" using 1:2@5
is equivalent to
> plot "a.dat" u 1:2,"a.dat" u 1:3,"a.dat" u
1:4,"a.dat" u 1:5
other example
> plot "a.dat" u 1:($2@3*2)
is equivalent to
> plot "a.dat" u 1:($2*2),"a.dat" u 1:($3*2)

One can olso specify steps by an other `@' parameter.
> plot "a.dat" u 1:2@5@2
is equivalent to
> plot "a.dat" u 1:2,"a.dat" u 1:4

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Thank you for your patch.

Much of this task can now be done natively in gnuplot. Only
the key step of iteration within a plot command is missing.
For example, to plot data from multiple files within a
single plot command one would hypothetically do:

# Get list of files
list = system("ls -1 *.dat")
# find out how many there are
nplots = words(list)
# define a function that returns the name of file i
file(i) = words(list,i)
# plot files 1 and 3 (only)
plot file(1), file(3)
#
# This is the missing component!
# No such command syntax currently exists,
# but it could be added
#
plot {i=1,nplots} file(i) using 1:2 with linespoints
#
# The same formalism could be used to iterate over
# fields within the same file:
#
plot {i=2,5} "data.dat" using 1:($i) with histograms

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I wonder why the following script produces "
internal error : non-STRING argument"?

# Get list of files
list = system("ls -1 *.dat")
# find out how many there are
nfiles = words(list)
# define a function that returns the name of file i
file(i) = words(list,i)
# plot files 1 and 3 (only)
#plot file(1), file(3)

# select files: from, step, to
a=system(sprintf("seq -f 'file(%%g)' -s , %g %g %g", 1, 1,
nfiles))

set macros
b="plot " . a
#b="plot " . file(1)
print b
@b

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Petr:

Because you have a typo in the definition of file(i).
It should be
file(i) = word(list,i)
not
file(i) = words(list,i)

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Well, now there is a problem: how to generate string
file(1) title file(1), file(2) title file(2)
? The -f in seq allows only one %g. Use awk instead?

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Here is a relatively small and simple-minded patch that
fills in the missing piece. It allows you to add an
iteration clause to the "plot" command. You can iterate over
anything, not just file names.

set style data lines
file(n) = sprintf("file_%d.dat",n)

plot for [i=3,6] "file.dat" using 1:(column(i))
plot for [k=1,99] file(k) using 1:2 title file(k)

set style data histogram
plot for [k=2,20] "datafile" using (column(k)) title col

Notes:

1) I'm not wild about the syntax, but this choice works
without having to change the token parser

2) Notice that the control variable can be named anything,
and that it can appear multiple times in the plot command

3) The is no support in this patch for multiple iterations
within the same command. I.e., you cannot do
plot for [i=1,2] file(i), for [j=6,7] file(j)

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In preparation for a code freeze and the run-up to a release of
version 4.2, existing bugs and patchsets are being prioritized.

This patchset is not on my (sfeam) list for inclusion in 4.2 and
is therefore being marked as priority 2.

Note that this does not mean it is a bad patch, or that it won't
be incorporated into cvs after 4.2 is released. We can
re-evaluate priorities after 4.2 is out.

If you want to argue for immediate reconsideration - go right
ahead; but do so quickly!

Ethan Merritt

• priority: 5 --> 2

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This version is a bit cleaner and contains documentation. It
allows one iteration specifaction per clause of the plot
command.

• priority: 2 --> 5

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I like this patch very very much, something I really needed
for ages!

I propose this syntax for enumeration (matlab/octave
compatible):

plot for [i=1:10] ...
plot for [i=1:2:10] ...

and, if possible,
plot for [i=3,5,8,13,21] ...

I wish to have this patch for 4.2. Thanks!

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The 30-Sep-2006 version re-arranges the code so that it can
be shared by 'plot' and 'splot'. Supporting splot required
adding a field to the iso_curves structure.

I thought about trying to support
plot for [i=3,5,8,foo,baz,etc]
but I'm not sure it's worth the effort to treat it as a
special case. You can already do
list = "3 5 8 ..."
item(j) = word(list,j)
plot for [j=1,n] file(item(j))
That doesn't quite work for the foo, baz, etc entries however.

I take it that for [i=1:2:10] means 1,3,5,7,9 ?
Is that a typo for [i=1:10:2]? The languages that I can
think of off the top of my head use the _third_ number as
the increment, not the second.

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> I take it that for [i=1:2:10] means 1,3,5,7,9 ?

Yes.

> Is that a typo for [i=1:10:2]?

No, 1:2:10 is correct in both Octave and Matlab:
octave> 1:2:10
ans =
1 3 5 7 9

> plot for [i=3,5,8,foo,baz,etc]
> list = "3 5 8 ..."
> item(j) = word(list,j)
> plot for [j=1:words(list)] file(item(j))

This is a good idea, please write it in docs. Its advantage is:
list='5 6'; replot

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More cleanup; plug a memory leak; change syntax to
plot for [i = start : end]
This makes it look much like a normal plot range specifier.

What is supposed to happen if one says
plot for [i = 1 : -2]

Syntax error?
Execute once and stop?
Don't execute at all?
Iterate in reverse order: 1, 0, -1, -2 ?

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> plot for [i = 1 : -2]

Don't plot at all. In order to use the reversed range, one
has to write
plot for [i=1:-1:-2]
The error syntax could be: "empty range, no data or function
to plot"

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I really like this patch. I have always wanted an easy way
to plot multiple indexes from a single file with different
line types (colors) without have to list each one
individually.

I think the proposed "plot for" syntax is good.

For whats is worth, Fortran90 uses a start:end:incr style
when accessing arrays.

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> Fortran90 uses a start:end:incr style

I prefer [start:end] and [start:incr:end] to be compatible
with Octave and Matlab.

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I think I would rather not add an increment at all. I'd
rather provide the simple iterator that's already coded
plot for [i=start:end]

and a truly general iterator
plot while [condition(i) next(i)] ...

To be used as follows:

next(i) = i+2
condition(i) = (i<10) && (i != 7)

plot i=3, while [condition(i) i=next(i)] ...

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Please add the increment. It is really a very very useful
feature.

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Gnuplot has longly been lacking the ability to plot a larger
amount of columns using a simple plot command. Ethan, your
iterator is really a good idea.

In the docs, I think it should read 'item(i)' instead of
'item[i]'.

Juergen

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OK. This version adds an optional increment
plot {for [i=<start>:<end>{:<incr>}} ...

If (start > end) it will issue a warning but not actually
skip the plot. I'd rather skip it, but to do so without
side-effects is non-trivial. Possibly we can stuff some
"don't draw me" flag in the plot header, but we'd still have
to figure out a way to avoid reading any associated data and
resetting the axis min/max ranges, etc.

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Few comments:

* plot for [i=10:-10:-1] x+i title sprintf('x**%i',i)
... I think this should go in reversed order, but it does
not. Could it go?

* please write in 'help plot iterat' that the
(a) start, end, inc are converted to integers (would it be
worth to support real numbers?),
(b) plot for the 1st iteration is always drawn (even for a
"wrong" interval)

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The problem with gracefully handling missing/empty plots is
now fixed [I think!] in cvs. See Bug 1579867.

Once I sorted that out, it became much easier to handle an
"empty" iteration by marking it NODATA; i.e. by pretending
it was a plot of an empty file. I suspect that there may
still be some side-effects on the auto-scaling code from the
scanning of files being skipped over, but the simple cases
now seem to work OK.

E.g.
plot sin(x), for [i=1:0] file(i), cos(x)
will now only plot sin(x) and cos(x), will not complain
about missing files, and will auto-scale as normal.

The 3D case is less tested than the 2D case. Please report
any problems.

plot-with-iteration code patch, docs, examples

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This version adds a separate demo "iterate.dem", and also
uses the new syntax to good advantage in "histograms.dem".

In the absence of late-breaking bug reports, I will put this
patchset into cvs sometime this weekend.

Special thanks to Janos Torok for inspiring this addition. I
didn't use your actual code, but the example provided by
your patch was key to motivating an equivalent more general
implementation.

As we gain experience with the simple form implemented here:
plot for [i=<start> : <end> { : <increment>}]
we can consider extending it to other forms of iteration. I
still lean toward adding
plot for [name in "A B C Q Y Z"] name.".dat" title name
but as we discussed already, the equivalent is already
possible using the somewhat longer version
list = "A B C Q Y Z"
item(i) = word(list,i)
and then iterating over i.