gnuplot computing stats over multiple columns - plot

Question

I have a simple 9 column file. I wan't to compute certain statistics for each column and then plot it (using gnuplot).
1) This is how I compute statistics for every column excluding the first one.
stats 'data' every ::2 name "stats"
2) In the output screen I can see that the operation is successful. Note that the number of columns/records is 8
* FILE:
Records: 8
Out of range: 0
Invalid: 0
Blank: 0
Data Blocks: 1
* COLUMNS:
Mean: 6.5000 491742.6625
Std Dev: 2.2913 703.4865
Sum: 52.0000 3.93394e+06
Sum Sq.: 380.0000 1.93449e+12
Minimum: 3.0000 [0] 490312.0000 [2]
Maximum: 10.0000 [7] 492643.5000 [7]
Quartile: 4.5000 491329.5000
Median: 6.5000 491911.1500
Quartile: 8.5000 492252.2500
Linear Model: y = 121.8 x + 4.91e+05
Correlation: r = 0.3966
Sum xy: 2.558e+07
3) Now I can access statistics on the first 2 columns by appending _x and _y like this
print stats_median_x
print stats_median_y
My questions are:
How can I access statistics (lets say medians) for the remaining 6 columns?
How could I plot lets say a line over all medians against some X axis?
I know that I can simply add a python script to pre-compute all this, but I would prefer to avoid it if there is an easy way to do it using gnuplot itself.
Thanks!

Answer 1

Short answer(s)
"How can I access statistics of the other column?"
with stats 'data'using n you will access to the nth column...
"How can I plot for example all medians?"
e.g. a set print and a do for cycle can create a data-file that you can use for the plot.
A working solution
set print "StatDat.dat"
do for [i=2:9] { # Here you will use i for the column.
stats 'data.dat' u i nooutput ;
print i, STATS_median, STATS_mean , STATS_stddev # ...
}
set print
plot "StatDat.dat" us 1:2 # or whatever column you want...
Some words more about it
Asking help to gnuplot itself with help stats it's possible to read a lot of interesting things :-).
Syntax:
stats 'filename' [using N[:M]] [name 'prefix'] [[no]output]]
This command prepares a statistical summary of the data in one or two columns of a file. The using specifier is interpreted in the same way as for plot commands. See plot for details on the index, every, and using directives.
From the first highlighted sentence we can understand that it prepares statistics for one or maximum two column each time (It's a pity let's see in future...).
From the second highlighted sentence it's possible to read that it will follow the same syntax of the plot command:
so stats 'data'using 3 will give you the statistic of the 3rd column in x
and stats 'data' using 4:5 of the 4th and 5th in x,y...
Notes about your interpretations
You said
This is how I compute statistics for every column excluding the first one.
stats 'data' every ::2 name "stats"
Not really this is the statistic for the first two column excluding the first two lines, indeed their counter starts from 0 and not from 1.
As consequence of the above assumption/interpretation, when we read
Records: 8
it means that the lines computed where 8; your file had 10 (usable) lines, you specify every ::2 and you skip the first two, thus you have 8 records useful for the statistic.
Indeed so we can better understand when in help stats it is said
STATS_records # total number of in-range data records
implying "used to compute this statistic".
Tested on gnuplot 4.6 patchlevel 4
Working on gnuplot Version 5.0 patchlevel 1