Python NumPy loadtxt 数据类型
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NumPy loadtxt data type
提问by Anastasia
I am trying to load a data set that looks like this:
我正在尝试加载一个如下所示的数据集：
Algeria,73.131000,6406.8166213983,0.1
Angola,51.093000,5519.1831786593,2
Argentina,75.901000,15741.0457726686,0.5
Armenia,74.241000,4748.9285847709,0.1
etc. At the end, I will need only columns 1 and 2. I won't need country names and the last column. Essentially, I need to extract two matrices with dimensions nx1. I know that I need to specify the data type:
等等。最后，我只需要第 1 列和第 2 列。我不需要国家/地区名称和最后一列。本质上，我需要提取两个维度为 nx1 的矩阵。我知道我需要指定数据类型：
data=np.loadtxt('file.txt',delimiter=',',dtype=[('f0',str),('f1',float),('f2',float),('f3',float)])
However, this produces a list of tuples,
然而，这会产生一个元组列表，
array([('', 73.131, 6406.8166213983, 0.1),
('', 51.093, 5519.1831786593, 2.0),`
instead of
代替
array(['',73.131,6406.8166213983,0.1],
['',51.093, 5519.1831786593, 2.0],
Where is the mistake?
错误在哪里？
采纳答案by atomh33ls
If you just want the first two columns you could use genfromtxt:
如果你只想要前两列，你可以使用genfromtxt：
import numpy as np
col1 = np.genfromtxt('yourfile.txt',usecols=(1),delimiter=',',dtype=None)
col2 = np.genfromtxt('yourfile.txt',usecols=(2),delimiter=',',dtype=None)
or both together:
或两者兼而有之：
np.genfromtxt('yourfile.txt',usecols=(1,2),delimiter=',',dtype=None)
回答by mamalos
Your "mistake" is that you set your own dtype. If you don't want the dtype you've set (where I see no reason why you wouldn't want it), you can use skiprows and usecols parameters of np.loadtxt() to ONLY load the columns you wish.
您的“错误”是您设置了自己的 dtype。如果您不想要您设置的 dtype（我看不出您为什么不想要它），您可以使用 np.loadtxt() 的 skiprows 和 usecols 参数来仅加载您希望的列。
Your result will be a NumPy array with a shape of (n, 2), not (n, 3) that you thought you'd have (where n is your number of rows).
您的结果将是一个形状为 (n, 2) 的 NumPy 数组，而不是您认为应该拥有的 (n, 3)（其中 n 是您的行数）。
