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ParameterGrid splits the string instead of combination

I'm trying to get the parameter grid for model selection. So, following the example in Sklearn documentation about ParameterGrid function we have this:

param_grid = {'a': [1, 2], 'b': [True, False]}
list(ParameterGrid(param_grid)) == (
                [{'a': 1, 'b': True}, {'a': 1, 'b': False},
                 {'a': 2, 'b': True}, {'a': 2, 'b': False}])

But what I want is pass only one value, without using list annotation ([]), like this:

param_grid = {'a': [1, 2], 'b': 'True', 'c': 'something'}

But then, list(ParameterGrid(param_grid)) just split all the strings instead of creation of two combinations. Result:

{'a': 1, 'b': 'T', 'c': 's'}
{'a': 1, 'b': 'T', 'c': 'o'}
{'a': 1, 'b': 'T', 'c': 'm'}

The question is, it's required to put all items in list format, or I'm missing something?

Solution

  • Yes, you need to use the [] notation, because the ParameterGrid expects the values to be an iterable. So when you set b as

    'b': 'True'

    It will iterate over the string 'True', hence you are getting different combinations with T, R, U and E.

    To fix this, use it like this

    param_grid = {'a': [1, 2], 'b': [True], 'c': ['something']}