merge , join , concat的区别
merge :
与sql 的join类似,有left join ,right join ,outer join , 连接字段可以是索引可以是一个列
join :
连接字段是索引,或者两个连接字段的列名一样。 其他 与merge 相同
merge is a function in the pandas namespace, and it is also available as a DataFrame instance method merge(), with the calling DataFrame being implicitly considered the left object in the join.
The related join() method, uses merge internally for the index-on-index (by default) and column(s)-on-index join. If you are joining on index only, you may wish to use DataFrame.join to save yourself some typing.
concat :
pandas 的内置的函数
https://blog.youkuaiyun.com/mr_hhh/article/details/79488445
有一种是类似于 sql 的union all,其余与pd.merge 相同
官方文档:
http://pandas.pydata.org/pandas-docs/stable/user_guide/merging.html