Numpy(Pandas)删除全为零的列的方法
在处理numpy数组,有这个需求,故写下此文:
使用np.argwhere和np.all来查找索引。要使用np.delete删除它们。
示例1
import numpy as np a = np.array([[1, 2, 0, 3, 0], [4, 5, 0, 6, 0], [7, 8, 0, 9, 0]]) idx = np.argwhere(np.all(a[..., :] == 0, axis=0)) a2 = np.delete(a, idx, axis=1) print(a2) """ [[1 2 3] [4 5 6] [7 8 9]] """
示例2
import numpy as np array1 = np.array([[1,0,1,0,0,0,0,0,0,1,1,0,0,0,1,1,0,1,0,0], [0,1,1,0,0,1,1,1,1,0,0,0,1,0,1,0,0,1,1,1], [0,0,1,0,0,1,1,1,0,0,0,0,0,0,0,1,0,0,1,1], [0,1,1,0,0,1,1,1,1,0,1,1,1,0,0,1,0,0,1,1], [0,0,1,0,0,1,1,1,0,1,0,1,1,0,1,1,0,0,1,0], [1,0,1,0,0,0,1,0,0,1,1,1,1,0,1,1,0,0,1,0], [1,0,1,0,1,1,0,0,0,0,1,0,0,0,1,0,0,0,1,1], [0,1,0,0,1,0,0,0,1,0,1,1,1,0,1,0,0,1,1,0], [0,1,0,0,1,0,0,1,1,0,1,1,1,0,0,1,0,1,0,0], [1,0,0,0,0,1,0,1,0,0,0,1,1,0,0,1,0,1,0,0]]) mask = (array1 == 0).all(0) column_indices = np.where(mask)[0] array1 = array1[:,~mask] print("raw array", array1.shape) # raw array (10, 20) print("after array",array1.shape) # after array (10, 17) print("=====x=====\n",array1)
其它查看:https://moonbooks.org/Articles/How-to-remove-array-rows-that-contain-only-0-in-python/
pandas 删除全零列
from pandas import DataFrame df1=DataFrame(np.arange(16).reshape((4,4)),index=['a','b','c','d'],columns=['one','two','three','four']) # 创建一个dataframe df1.loc['e'] = 0 # 优雅地增加一行全0 df1.ix[(df1==0).all(axis=1), :] # 找到它 df1.ix[~(df1==0).all(axis=1), :] # 删了它
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