Pandas knowledge points - add operation append

stay Pandas in ,append() Method is used to convert one or more DataFrame or Series Add to DataFrame in .append() Method can also be used for merge operations , In this paper, append() Method usage .

One append() To achieve a merger

append(other): Put one or more DataFrame Add to call append() Of DataFrame in , Realize the function of merging ,other Parameters are passed into the merged DataFrame, If you need to add more than one DataFrame, Then pass in a list or tuple .

append() Method realizes the function of merging by adding , This merge function is by line ( The longitudinal ) To merge , The number of rows of the merged result is all DataFrame Sum of rows .

Two Fill in nonexistent columns

If the append() Of DataFrame And incoming append() Of DataFrame There are different columns in , After adding, null values will be filled in the nonexistent Columns , So even if two DataFrame Having different columns does not affect the addition operation .

3、 ... and Add multiple DataFrame

Add multiple DataFrame when , Pass in multiple... As a list or tuple DataFrame that will do , The added principle remains the same . if necessary , You can batch DataFrame Merge into one DataFrame.

Four Reset row index

ignore_index: ignore_index The parameter defaults to False, The row index of the result remains the original DataFrame Row index in , Even if the same row index exists, it is not affected . take ignore_index It is amended as follows True, The row index of the result is reset from 0 Integer index to begin with .

verify_integrity: verify_integrity The parameter defaults to False, Added DataFrame When there are the same row indexes in , You can keep the original results . take verify_integrity It is amended as follows True, If you add DataFrame There are the same row indexes in , Will throw out ValueError. Set up verify_integrity Parameter is True, To avoid duplicate row indexes in the results , But it is likely to cause the addition to fail , Therefore, we need to first observe whether the original data is suitable for .

ignore_index and verify_integrity When used at the same time ,ignore_index Sir , So when two parameters are used at the same time , Does not throw an exception .

5、 ... and add to Series

append() Methods can also be used in DataFrame Add Series. add to Series when , To put ignore_index Parameter set to True Or to Series Set up name Parameters , Otherwise it will throw TypeError, as a result of Series No names .

Set up ignore_index Parameter is True Will reset the row index of the result , It's added like this Series As a line in the result , The row index will be generated automatically .

Appoint Series Of name Parameters , such Series Will be with name Parameters are added as row indexes to DataFrame in . Even if the designated name Value and DataFrame Duplicate row index in , You can also successfully add (verify_integrity Not for True).

6、 ... and summary

As of this article , This series introduces five methods that can be used for merge operations ：concat()、merge()、join()、combine()、append(), Summarize their usage differences .

concat(): Connection operation , Can connect multiple DataFrame, You can set whether to merge by row or column . Yes inner、outer、left、right Four different connection modes . You can set the index of the result , In particular, there are many ways to deal with multiple row indexes .

merge(): Merge operation , Can only be used to merge two DataFrame, And they are merged by column , Only when two DataFrame The effect of merging by row is only when the column names of are exactly the same . Merge according to the specified join column ( Or row index ) And connection mode to match two DataFrame The line of . You can set the suffix of the same column name and display whether the connected column is in two columns in the result DataFrame There's always .

join(): Join operation , Can be in a DataFrame Add more than one DataFrame, The results are merged by column . Merge according to the specified join column ( Or row index ) And connection mode to match two DataFrame The line of , You can also set the suffix of the same column name , So sometimes join() and merge() They can switch to each other .

combine(): Joint operation , For two DataFrame, Join by column . Joint operation is to put a DataFrame Part of the data in the uses another DataFrame Replace or supplement the data in , A function is used to define the rules for fetching data during Union . Null values can also be populated during Union .

append(): Add operation , Multiple DataFrame Add to a DataFrame in , Add by line . The add operation simply adds multiple DataFrame Splice together in rows , You can reset the row index .