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One of the most common operations related to pandas is joining data frames together. This is because data frames often hold different kinds of information about the same entity and can be linked by some common feature or column. To do this, pandas has several functions such as concat(), merge() and join().

The merge() function allows us to combine two DataFrames? in a variety of ways. It can perform an inner join, outer join or cross join. Inner joins are based on the intersection of each row in the calling frame with each column in the other frame. Outer joins are based on the leftmost and rightmost rows in the calling frame that match each column in the other frame. Cross joins are a cartesian product of each pair of DataFrames?, which preserves the ordering of their key columns.

Some other parameters are available for merge(), such as on, lsuffix and rsuffix, which allow you to add suffixes to any overlapping columns and specify how to order the result DataFrames?. These options are not available when passing a list of other DataFrames?.

When a column or index in a DataFrame? is shared by two other DataFrames?, it can be joined with those DataFrames? using the join() method. https://join-pd.org/ The on, how, lsuffix, rsuffix, and sort parameters are all optional.

The on parameter specifies the field or index to join on. It must be present in both DataFrames? and must be an integer, datetimelike, or float type. The lsuffix and rsuffix parameters allow you to append a identifier to duplicated column names in the resulting DataFrame?, making it easier to keep track of the origins of column names. The sort parameter allows you to sort the resulting DataFrame? by the join key if desired.

Another important thing to remember about joins is that they always return an unordered DataFrame? if you leave out the how parameter. This means that if you do a LEFT OUTER JOIN with the first table (table A) and then a RIGHT OUTER JOIN with the second table (table B), all rows in the resulting DataFrame? will be listed with all possible values for the join key. This can be confusing, but it is essential for all data analysis. Fortunately, there is a tool called joinpd that helps to alleviate this confusion. Joinpd is an open source tool that provides a graphical interface to perform joins on multiple tables or DataFrames? in a database. This tool makes it easy to create complex JOINs. It is free to use, and you can download it here. Using the tool can help you make your work more efficient and organized. It can also save you a lot of time.


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Last-modified: 2023-10-21 (土) 18:04:30 (201d)