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Date: Fri, 20 Feb 2015 11:55:28 -0800 (PST)
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Subject: Scatter plot from a binary data
From: maksym.petrenko@gmail.com
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Xref: csiph.com comp.graphics.apps.gnuplot:2772

Hi guys, I'm trying to marry nco tools and gnuplot to produce a scatter plo=
t of some fairly large data. A short version of the question is this. Given=
 a binary file of 4 float numbers:

#X1#X2#Y1#Y2


I'd like to build a scatter plot that has points (x:X1,y:Y1), (x:X2,y:Y2). =
I tried several things, like this for example:


plot 'scatter00' binary record=3D(2):(2) format=3D"%float" using 1:2 lc rgb=
 'blue' title ''=20


However, all of them seem to produce a version of (x:X1,y:X2), (x:Y1,y:Y2).=
 I wonder if there is a way to tell gnuplot the file contains ALL elements =
of X followed by ALL elements of Y, rather than pairs of Xn,Yn?



A long version of the question:

As an input, I have an .nc file with two FLOAT variables, x and y, of the s=
ame size - say 100,000,000 points each. Since gnuplot does not work with .n=
c files directly, I need to somehow serialize the file. My current approach=
 is to dump each x and y to separate text files using ncks, each file essen=
tially a column of float numbers, and then merge these files into a single =
two-column CSV-like file using Unix 'paste'. While dumping takes about a mi=
nute, merging takes about 2-3 minutes. Plotting takes about 5 seconds. Now,=
 the reason I need to merge the two files is because gnuplot expects the in=
put data to be in a form of records:

X1 Y1
X2 Y2
...
Xn Yn

In the same time, ncks can dump data only sequentially, either to separate =
files or to a single file:=20
X1
X2
...
Xn
Y1
Y2
...
Yn

I then tried to dump to a binary file with an idea that gnuplot can read in=
 the binary file as an array and manipulate it according to rows/columns. A=
gain, ncks gives me something like this:

(#X1#X2...#Xn#Y1#Y2...#Yn)

Gnuplot, on the other hand, expects something like this:

(#X1#Y1#X2#Y2...)

When I try this command:

plot 'scatter00' binary record=3D(600000):(600000) format=3D"%float" using =
1:2 lc rgb 'blue' title ''=20

I expect gnuplot to read in 600000 elements of X followed by 600000 element=
s of Y. However, what happens is gnuplot still reads X1,Y1,X2,Y2...X600000,=
Y600000. Is there a way to modify the command to read in the original data =
without reshuffling the bytes?

many thanks,
Maksym