On Fri, Jul 31, 2020 at 10:59 PM Steven D'Aprano <steve@pearwood.info> wrote:
[...]
The first request in this thread was from Hans:
https://mail.python.org/archives/list/python-ideas@python.org/message/S7UMTW...
He is using a dict to hold an array of columns indexed by name `{column_name: column}` and wanted to re-order and insert columns at arbitrary positions.
Pandas solves for columnar data. SQL is one source and destination for columnar data which Pandas supports. Pandas handles NULL/None/NaN more consistently than dict.get("key", None). https://pandas.pydata.org/pandas-docs/stable/user_guide/io.html#io-sql https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#return... assert df.columns.tolist() == ['a', 'b', 'c'] # this creates a copy df2 = df[['b', 'c', 'a']] # this doesn't create a copy df.reindex(columns=['b', 'c', 'a']) # this inserts a column after column b df.insert(df.columns.get_loc('b'), 'newcolumn', df['c']) df.insert(df.columns.tolist().index('b'), 'newcolumn2', df['c']) https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.... https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.... If you need to reorder rows (or columns transposed (df.T)), you could select with .loc[[list, of, indexvalues]] or .iloc[[list, of, ints]] http://www.datasciencemadesimple.com/reindex-python-change-order-column-rows... ... To accomplish the same with the Python standard library, you'd need to create a data structure that is an amalgamation of list and dict: a MutableMapping with a Sequence interface for at least .keys() (or .keyseq()). Is there already a "pure python" Dataframe? Do whatever you want, but the Pandas DataFrame API is also available in Dask, Modin, and CuDF; for distributed and larger-than-RAM use.