Plot data and fit-functions of multiple files into one plot

Question

I have N input files and I want to plot the data of these files together with their fit function into one single plot (i.e. one plot for all files, data and fit-function).

After a long time of fiddling I found a solution (see below), but I find it "cumbersome and ugly" and I'm wondering if there is a better, more elegant way of achieving the same thing.

I should say that I'm on gnuplot 5.0 under Windows. The test script below doesn't specify a terminal (I'm testing with windows and wxt), but the final script will use pngcairo terminal.

Things that I find sub-optimal about my solution:

I need two intermediary tables $data and $fit. My original attempt was to use a do for{} loop to read each file in turn perform the fit and generate the plot, but that didn't work out.
Rather than using a fit function, I plot the fit curve (in this simple case a straight line) as data into a table. I experimented with creating on-the-fly user functions using eval but just couldn't quite figure it out (especially how to keep them in sync with the data).
I want the fit-equation to be displayed in the chart. I do this by setting labels, but it would be nicer if it would just be part of the key.

My test data:

data1.dat
100 0.15
200 0.29
300 0.46
400 0.58

data2.dat
100 0.12
200 0.22
300 0.35
400 0.48

data3.dat
100 0.1
200 0.22
300 0.29
400 0.40

My gnuplot script:

set key left
set xrange [0:*]
set yrange [0:0.5]

# user function for linear fit
lin(x) = slope * x + offset
max(a,b) = ((a>=b)? a : b)

file_list = "data1 data2 data3"

x_max = 0
# first write all data of interest into a (memory) table
set table $data
do for [name in file_list] {
  filename = name . ".dat"
  plot filename u 1:2
  print ""
  print ""
  x_max = max(GPVAL_DATA_X_MAX, x_max)
}
unset table
x_max = max(GPVAL_DATA_X_MAX, x_max)

num_indices = words(file_list)

# now calculate a linear fit for each dataset
set sample 2
set table $fit
do for [i = 0:(num_indices-1)]{
  fit lin(x) $data index i using 1:2 via slope, offset
  plot [0:x_max][0:0.5] lin(x)
  set label (i+1) sprintf("%s = %.3g*x + %.3g", word(file_list, i+1)."(x) ", slope, offset) at 200,(0.20 - 0.05*i)
}
unset table

set title "Data and Linear Fit"
set xlabel "x"
set ylabel "y"

#now we got both data and fit for all files, plot everything at once
plot for [i = 0:(num_indices-1)] $data index i title word(file_list,i+1) with points lc i+1, for [i = 0:(num_indices-1)] $fit index i with lines lc i+1 noti

Plot data and fit-functions of multiple files into one plot

Answers (1)

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