Pandas合并_concat

df1 = pd.DataFrame(np.ones((3,4))*0,columns=['a','b','c','d'])
df2 = pd.DataFrame(np.ones((3,4))*1,columns=['a','b','c','d'])
df3 = pd.DataFrame(np.ones((3,4))*2,columns=['a','b','c','d'])

#上下合并
res = pd.concat([df1,df2,df3],axis=0,ignore_index=True)   #axis=0竖向合并,ignore_index=True忽略原排序，重新排序
print(res)   

#join, ['inner','outer']  
df4 = pd.DataFrame(np.ones((3,4))*0,columns=['a','b','c','d'],index=[1,2,3])
df5 = pd.DataFrame(np.ones((3,4))*1,columns=['b','c','d','e'],index=[2,3,4])
print(df4)
print(df5)
res = pd.concat([df4,df5],join='inner')  #inner裁剪，只合并两者都有部分，默认Outer没有部分NaN填充
print(df4.index)
# res = pd.concat([df4,df5], axis=1, join='inner',join_axes=[df4.index]) 
# join_axes已经过期，上一句运行会提示出错，可以用reindex实现相同结果
res = pd.concat([df4,df5.reindex(index=df4.index)],axis=1) 
print(res)

res= df4.append(df5,ignore_index=True)  #append向下拼接