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pythonlistimportiterable-unpacking

Python: loading text with 3 columns of data

I have a text file with 3 columns of data I want to plot.

from numpy import *
import pylab
from mpl_toolkits.mplot3d import Axes3D

datalist = loadtxt("datagrid.txt")
x, t, u = datalist[:, 0, 0], datalist[0, :, 0], datalist[0, 0, :]

fig = pylab.figure()
ax = fig.add_subplot(111, projection = '3d')
ax.plot(x, t, u)
pylab.show()

I am told too many indices. How can I unpack a text file with 3 columns if I can only use 2 indices?

Solution

  • As I understand correctly, the file "datagrid.txt" contains something like

    1 2 3
4 5 6
7 9 0
. . .
. . .
. . .

    If so, then loadtxt loads it as two-dimensional array. Hence, you need to change the line setting x, t, and u into:

    x, t, u = datalist[:,0], datalist[:,1], datalist[:,2]

    or even simpler and more Pythonic:

    x, t, u = datalist.transpose()

    or as the third option, read your file as:

    x, t, u = loadtxt("datagrid.txt", unpack=True)