[ENH] Add ability to enforce specific filter on Google Analytics query

[manugarri]

Fix for #3505

This PR allows to directly write filters to ga.py read_ga function.

Currently only OR filters are supported. with this PR we can support directly writing the filters as a string, allowing for example AND filtering.

Example here

[jreback]

It seems that you can already do this, by simply specifying the filters as a compound string, no?

have multiple keywords for this does not seem like a good idea.

Further, this needs tests (well the entire module needs some tests, against a mock GA).

[manugarri]

So currently you can only add filters that get added with a comma separating them (see https://github.com/pydata/pandas/blob/master/pandas/io/ga.py#L386).

comma separated filters are interpreted as being added with an OR. The Google analytics way of adding an AND to the filters is by adding the filter with a semicolon separating them.

My implementation doesn't affect the current API (afaik), and allows anyone with more specific filtering needs to write a custom filter.

[jreback]

and is their anything stopping you from simply passing the entire correct string as the filter argument?

[manugarri]

ok, so just noticed that my implementation was a totla overkill.

you can just send the raw_filter as filter = ['filter1;ga:filter2,ga:filter3...]

Will close