Fix for issue skipped_columns not working #15947

[Devanshusisodiya]

Closes #15947

The changes done in frame.py have been validated with the required tests of H2OFrame being tested in /h2o-py/tests/testdir_apis/Data_Manipulation/pyunit_h2oH2OFrame.py

skipped_columns parameter is now functional and all tests are passing.

[Devanshusisodiya]

@wendycwong @tomasfryda please review this pr.

[tomasfryda]

Thank you @Devanshusisodiya for spending time on this issue. Unfortunately, your solution doesn't seem to me to be valid. Please don't be discouraged, H2O-3 doesn't have code base that's easy to contribute to.

[tomasfryda]

This ignores the skipped columns so in some cases the skipped column is present in the resulting frame.

Let's have a frame:

| a | b | c |
+---+---+---+
| 1 | 2 | 3 |
| 4 | 5 | 6 |

and if we have skipped_columns=[0,1], then we would get just:

| a |
+---+
| 1 | 
| 4 |

but I would expect to get:

| c |
+---+
| 3 |
| 6 |

Also note that it's likely that skipped_columns should support inputs that are column indices (List[int]) or column names (List[str]).

[Devanshusisodiya]

@tomasfryda I understand your point, nevertheless i understand the problem and will try to solve it.

Are there any other cases I should be aware of?

[tomasfryda]

You should also make sure you modify the csv writing accordingly, so that only those columns that are not skipped are written. And please write a test for those cases when there's skipped_columns are at the beginning, the end, and in the middle (and possibly more cases depending on your actual implementation).

And while you're at it, you can also improve the code so that it makes sure that the tmp_path is removed, e.g.:

tmp_handle, tmp_path = tempfile.mkstemp(suffix=".csv")
try:
    .....
finally:
    os.remove(tmp_path)

[Devanshusisodiya]

@tomasfryda I made more changes based on the requirements and the original issue description. Also I think there is no need to make any in change csv writing because it takes the updated column_names as argument.

Please correct me if I'm wrong