python 把几个DataFrame合并成一个DataFrame——merge,append,join,conca
pandas provides various facilities for easily combining together
Series, DataFrame, and Panel objects with various kinds of set logic for
the indexes and relational algebra functionality in the case of join /
merge-type operations.
1、merge
pd.merge(left, right, how='inner', on=None, left_on=None, right_on=None,
left_index=False, right_index=False, sort=True,
suffixes=('_x', '_y'), copy=True, indicator=False)
对象
对象
键
综合
综合
数目
left_index
︰
情况下
'_y')。
copy︰。
。
1.result = pd.merge(left, right, on='key')
2.result = pd.merge(left, right,on=['key1', 'key2'])
3.result = pd.merge(left, right, how='left', on=['key1', 'key2'])
4.result = pd.merge(left, right, how='right', on=['key1', 'key2'])
5.result = pd.merge(left, right, how='outer', on=['key1', 'key2'])
2、append
1.result = df1.append(df2)
2.result = df1.append(df4)
3.result = df1.append([df2, df3])
4.result = df1.append(df4, ignore_index=True)
4、join
left.join(right, on=key_or_keys)
pd.merge(left, right, left_on=key_or_keys, right_index=True,
how='left', sort=False)
1.result = left.join(right, on='key')
2.result = left.join(right, on=['key1', 'key2'])
3.result = left.join(right, on=['key1', 'key2'], how='inner')
4、concat
pd.concat(objs, axis=0, join='outer', join_axes=None, ignore_index=False,
keys=None, levels=None, names=None, verify_integrity=False,
copy=True)
。
。
。
。
。
keys︰。
。
。
。
副本。
1.frames = [df1, df2, df3]
2.result = pd.concat(frames)
3.result = pd.concat(frames, keys=['x', 'y', 'z'])
4.result.ix['y']
A B C D
4 A4 B4 C4 D4
5 A5 B5 C5 D5
6 A6 B6 C6 D6
7 A7 B7 C7 D7
5.result = pd.concat([df1, df4], axis=1)
6.result = pd.concat([df1, df4], axis=1, join='inner')
7.result = pd.concat([df1, df4], axis=1, join_axes=[df1.index])
8.result = pd.concat([df1, df4], ignore_index=True)