import pandas as pd
import numpy as np
 
a=np.array([[1,2,3],[4,5,6],[7,8,9]])
df1=pd.DataFrame(a,index=['row0','row1','row2'],columns=list('ABC'))
print(df1)
df2=df1.copy()
 
#删除/选取某列含有特定数值的行
#df1=df1[df1['A'].isin([1])]
#df1[df1['A'].isin([1])] 选取df1中A列包含数字1的行
 
df1=df1[~df1['A'].isin([1])]
#通过~取反，选取不包含数字1的行
print(df1)

#删除/选取某行含有特定数值的列
cols=[x for i,x in enumerate(df2.columns) if df2.iat[0,i]==3]
#利用enumerate对row0进行遍历，将含有数字3的列放入cols中
print(cols)
 
#df2=df2[cols]  选取含有特定数值的列
df2=df2.drop(cols,axis=1) #利用drop方法将含有特定数值的列删除
print(df2)

import pandas as pd
import numpy as np
 
df1 = pd.DataFrame(
  [
    [np.nan, 2, np.nan, 0],
    [3, 4, np.nan, 1],
    [np.nan, np.nan, np.nan, 5],
    [np.nan, 3, np.nan, 4]
  ],columns=list('ABCD'))
print(df1)
df2=df1.copy()
 
df1['A']=df1['A'].fillna('null') #将df中A列所有空值赋值为'null'
print(df1)
df1=df1[~df1['A'].isin(['null'])]
print(df1)
 
#删除某行空值所在列
 
df2[0:1]=df2[0:1].fillna('null')
print(df2)
cols=[x for i,x in enumerate(df2.columns) if df2.iat[0,i]=='null']
print(cols)
df2=df2.drop(cols,axis=1)
print(df2)