ENH: concat & merge: return True if left DataFrame is modified
Hi,
This ticket is to propose 2 changes:

1st change: make available `concat` as method of DataFrame (similar to `merge`)
Concat could accept a list of DataFrame, similar to `pd.concat`.

2nd change: whichever `pandas.DataFrame.merge` or (newly implemented) `pandas.DataFrame.concat`
- modify left DataFrame in place
- return a boolean:
   - `True`if left DataFrame has actually been modified
   - `False`if left DataFrame has actually not been modified

Such a feature would prevent the user to make a check `pandas.DataFrame.equals()` to know if the left DataFrame has been modified or not.
Personnally, in my case, the left DataFrame can be a DataFrame I am just reading from a data file, and the right DataFrame, some 'new data' I am thinking it is new and needs to be merged/concatenated to the existing one.

If my merge/concat processing do not result in any change, I will not overwrite the same DataFrame on disk (useless: it has not been modified)

Could this be considered?
Thanks for your help.
Bests