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Here’s a detailed guide to gnuplot with a focus on multi-column data handling, customization, and advanced plotting features:

1. Basic Multi-Column Plotting

Assume you have a data file data.txt with multiple columns:

# X    Y1    Y2    Y3
1    2     5     8
2    3     6     9
3    4     7     10

Plot a Single Column:

plot "data.txt" using 1:2 with lines  # Plot X (col1) vs Y1 (col2)

Plot Multiple Columns:

plot "data.txt" using 1:2 with lines, \
     "data.txt" using 1:3 with points, \
     "data.txt" using 1:4 with linespoints
# Plots col1 vs col2 (lines), col1 vs col3 (points), col1 vs col4 (lines+points)

Combine Columns in Math Operations:

plot "data.txt" using 1:($2+$3) with lines  # Plot X vs (Y1 + Y2)

2. Multi-Column Data from a Single File

Plot Multiple Columns Against the Same X:

plot "data.txt" using 1:2, "" using 1:3, "" using 1:4
# The `""` reuses the previous filename (data.txt)

Label Columns with Titles:

plot "data.txt" using 1:2 title "Y1", \
     "" using 1:3 title "Y2", \
     "" using 1:4 title "Y3"

3. Plotting Multiple Files

If you have two files, data1.txt and data2.txt:

plot "data1.txt" using 1:2 with lines, \
     "data2.txt" using 1:3 with points

4. Error Bars (Using Multiple Columns)

For data with errors (e.g., X Y Y_error):

# X    Y    Y_err
1    2     0.5
2    3     0.6
3    4     0.7

Plot with error bars:

plot "data.txt" using 1:2:3 with yerrorbars

5. Data Manipulation with using

Column Arithmetic:

plot "data.txt" using 1:(log($2))  # Plot log(Y1)

Select Columns by Index:

Columns are referenced as $1, $2, etc. (1-based indexing):

plot "data.txt" using ($1):($2/$3)  # Plot X vs (Y1/Y2)

6. Multiplot (Subplots)

Arrange multiple plots in one figure:

set multiplot layout 2,1  # 2 rows, 1 column
plot "data.txt" using 1:2  # Top plot
plot "data.txt" using 1:3  # Bottom plot
unset multiplot

7. Customization

Labels, Titles, and Ranges:

set xlabel "X-axis"
set ylabel "Y-axis"
set title "Multi-Column Plot"
set xrange [0:5]
set yrange [0:10]

Line Styles and Colors:

plot "data.txt" using 1:2 with lines lt rgb "red" lw 2, \
     "" using 1:3 with points pt 7 ps 1.5 lc "blue"
# lt = linetype, lw = linewidth, pt = point type, ps = point size

8. Save Plots to Files

set terminal pngcairo enhanced  # High-quality PNG
set output "plot.png"
plot "data.txt" using 1:2 with lines
set terminal wxt  # Switch back to interactive window (if needed)

9. Advanced: Statistical Operations

Calculate averages or sums:

stats "data.txt" using 2  # Compute stats for column 2 (Y1)
print STATS_mean  # Print the mean of Y1

Example Workflow

  1. Data File (data.txt):

    # Time   Temperature   Pressure   Humidity
0       25            1010       60
1       26            1005       58
2       27            1000       55

  2. Gnuplot Commands:

    set xlabel "Time (hours)"
set ylabel "Temperature (°C)"
set y2label "Pressure (hPa)"  # Second y-axis
set y2tics  # Enable second y-axis
plot "data.txt" using 1:2 with lines axes x1y1 title "Temperature", \
     "" using 1:3 with lines axes x1y2 title "Pressure"

Key Tips

  • Use help [command] in gnuplot for documentation (e.g., help plot).
  • Column indices start at 1 ($1, $2, etc.).
  • Combine columns with math: ($2 + $3), ($4/$5), etc.
  • Use \ to split commands across lines.

With these tools, you can handle multi-column data, customize plots, and create publication-quality figures in gnuplot!