ENH: other join types than 'left' for .update

[maxgrenderjones]

Running 0.15.1

DataFrame.update(other, join='left', overwrite=True, filter_func=None, raise_conflict=False)
    Modify DataFrame in place using non-NA values from passed DataFrame. Aligns on indices

    Parameters :    
    other : DataFrame, or object coercible into a DataFrame
    join : {‘left’, ‘right’, ‘outer’, ‘inner’}, default ‘left’

But..

C:\Anaconda\lib\site-packages\pandas\core\frame.pyc in update(self, other, join, overwrite, filter_func, raise_conflict)
   3292         # TODO: Support other joins
   3293         if join != 'left':  # pragma: no cover
-> 3294             raise NotImplementedError("Only left join is supported")
   3295 
   3296         if not isinstance(other, DataFrame):

NotImplementedError: Only left join is supported

[jorisvandenbossche]

Yes, the docs should better mention that (care to do a PR?)

Or we should implement it of course.

[jorisvandenbossche]

Closed by #8912

[jreback]

I left this open for an eventual impl

[jorisvandenbossche]

@jreback ok, changed the title and labels to reflect that then

[debnathshoham]

Hi, I want to pick this up. But I am a little confused about how right, inner and outer would behave.

In df1.update(df2, join)

1. Would df2 change for join=right?
2. For join=inner, df1 would retain only the common indices
3. For join=outer additional indices from df2 would be added to df

Maybe some example about the expecetd behaviours would be really helpful.

[pascal456]

I looked for a solution that would do something like what I would expect to achieve with

.update(other, join='outer')

But after a while I realized that ther is already
pandas.DataFrame.combine_first

So, when I am not mistaken, the case join='outer' is already implemented.

Assumption: you apply this in the correct order. Since with .update, I expect other to overwrite the original, while combine_first keeps the original value, if there are values in both the DataFrames. Which means you would rather say outer.combine_first(original).

Thoughts on this? This should be added to the docs I would say. Took me while to realize this.