Numpy 将 txt 文件导入为没有文本行的矩阵

Question

I have a txt file like the following, where I want to import the last column without the text so that I can do matrix vector operations with it

Node Number X Location (mm) Y Location (mm) Z Location (mm) Imported Initial Strain (mm/mm) 
1   54.545  29.798  7.3281  9.8534e-003 
2   53.976  28.979  7.2569  5.9253e-003 
3   68.579  16.26   7.3473  7.0993e-003 
4   67.902  16.955  7.3363  5.9801e-003 

I tried numpy.loadtxt("path")[1:,4] but get the following error which I assume is due to the text inside my txt file

ValueError: could not convert string to float: 'Node'

Answer 1

You might use numpy.genfromtext which allow ignoring starting line(s) with skip_header , so it your case:

import numpy as np
arr = np.genfromtxt("file.txt", skip_header=1)

should create numpy.ndarray from data from file.txt . Beware that in older versions of NumPy there is skiprows rather than skip_header in genfromtxt function (see linked docs for details).

Answer 2

Numpy loadtxt has a number of parameters:

• skiprows allows to skip the initial rows
• usecols allows to only load a selection of columns

Here what you want is:

arr = np.loadtxt(io.StringIO(t), skiprows=1, usecols=4)

With the sample data, it gives as expected:

array([0.0098534, 0.0059253, 0.0070993, 0.0059801])