python - Delete lines in a dataframe based on lookup in another dataframe -


i work 2 dataframes. want remove lines in first dataframe based on match in one.

in df1 have 2 columns (called type1 & type2) + flag. want delete lines flag = true & type1 & type2 match combination in df2.

import pandas pd import numpy np df1 = pd.dataframe(np.random.randint(0,10,size=(100, 2)),columns = ["type1","type2"]) df1["flag"] = np.random.randint(0,10,size=(100))>6 df1.head()    type1  type2   flag 0      8      5  false 1      1      6  false 2      9      2  false 3      0      9   true 4      2      9  false  df2 = pd.dataframe(np.random.randint(0,10,size=(100, 2)),columns = ["type1","type2"]) df2.head()    type1  type2 0      0      9 1      7      8 2      5      1 3      3      3 4      3      2

for example here line in df1 index=3 should deleted flag=true , (0,9) exists in df2.

use merge 1 df , filter boolean indexing - need values in df1 (left_only) , false in flag, rows both true deleted.

#on parameter omitted if matched column same in both df  df3 = pd.merge(df1, df2, how='left', indicator=true) #if multiple matched columns #df3 = pd.merge(df1, df2, how='left', indicator=true, on = ['type1','type2']) print (df3)    type1  type2   flag     _merge 0      8      5  false  left_only 1      1      6  false  left_only 2      9      2  false  left_only 3      0      9   true       both 4      2      9  false  left_only  df3 = df3.loc[(df3['_merge'] == 'left_only') & (~df3['flag']), ['type1','type2']] print (df3)    type1  type2 0      8      5 1      1      6 2      9      2 4      2      9

also possible create mask , filter df1 (if many columns):

m = (df3['_merge'] == 'left_only') & (~df3['flag']) df1 = df1[m] print (df1)    type1  type2   flag 0      8      5  false 1      1      6  false 2      9      2  false 4      2      9  false

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