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I want to plot a coloured contour graph with x,y,z from 3 columns of a comma delimited text file, but each time I try the code below, I get ValueError: too many values to unpack (expected 3) error. I would be grateful if that could be resolved.

I would also like to know if there is another (probably better) code for plotting the 3 independent columns.

This is the code:

from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt
from matplotlib import cm
import numpy as np
import scipy.interpolate

N = 100000

long_col, lat_col, Bouguer_col = np.genfromtxt(r'data.txt', unpack=True)

xi = np.linspace(long_col.min(), long_col.max(), N)
yi = np.linspace(lat_col.min(), lat_col.max(), N)
zi = scipy.interpolate.griddata((long_col, lat_col), Bouguer_col, (xi[None,:], yi[:,None]), method='cubic')


fig = plt.figure()
plt.contourf(xi, yi, zi)
plt.xlabel("Long")
plt.ylabel("Lat")
plt.show()

This is the 'data.txt' sample data.

Lat, Long, Elev, ObsGrav, Anomalies
6.671482000000001022e+00,7.372505999999999560e+00,3.612977999999999952e+02,9.780274000000000233e+05,-1.484474523360840976e+02
6.093078000000000216e+00,7.480882000000001142e+00,1.599972999999999956e+02,9.780334000000000233e+05,-1.492942383352201432e+02
6.092045999999999850e+00,7.278669999999999973e+00,1.462445999999999913e+02,9.780663000000000466e+05,-1.190960417173337191e+02
6.402087429999999912e+00,7.393360939999999992e+00,5.237939999999999827e+02,9.780468000000000466e+05,-8.033459449396468699e+01
6.264082730000000154e+00,7.518244540000000420e+00,2.990849999999999795e+02,9.780529000000000233e+05,-1.114865156192099676e+02
6.092975000000000030e+00,7.482914000000000065e+00,1.416474000000000046e+02,9.780338000000000466e+05,-1.525697779102483764e+02
6.383570999999999884e+00,7.289616999999999791e+00,2.590403000000000020e+02,9.780963000000000466e+05,-8.300666170357726514e+01
6.318417000000000172e+00,7.557638000000000744e+00,1.672036999999999978e+02,9.780693000000000466e+05,-1.246774551668204367e+02
6.253779999999999895e+00,7.268805999999999656e+00,1.059429999999999978e+02,9.781026999999999534e+05,-9.986763240839354694e+01
6.384635000000000282e+00,7.291032000000000401e+00,2.615624000000000251e+02,9.780963000000000466e+05,-8.256190758384764194e+01
Olatoye
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  • The error comes from the fact that you have more than three columns in your data file but try to unpack it to 3 columns. Instead try to unpack it to 5 variables, e.g. `Lat, Long, Elev, ObsGrav, Anomalies = np.genfromtxt(r'data.txt', unpack=True)`. After that you need to provide 2D arrays to `contourf`. There are enough questions and answers on how to do that around. – ImportanceOfBeingErnest Nov 29 '17 at 12:20
  • It returned **ValueError: too many values to unpack (expected 5)** error – Olatoye Nov 29 '17 at 12:32

1 Answers1

1

If the data file looks exactly like in the question you first of all have 5 columns, which you cannot unpack to 3 variables.
Next, you have a header line which you do not want to be part of the data. Also the header line is separated by ,<space>, while the data is separated by ,.

So in total you need

import numpy as np

a,b,c,d,e = np.genfromtxt("data.txt", unpack=True, delimiter=",", skip_header=1)
ImportanceOfBeingErnest
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