python pandas dynamic query pass into function

Question

I have the dataframe with columns of strings. I want to use a part of it in some function. A part to be used is defined by condition which passed into function.

def myfunc(condition):
    tmp_df = df[condition].copy()

    #doing something else wit tmp_df

    return some_result

My questions are:

How can I pass condition for string columns? For example:

df.str_column.str.len()>10
How to pass an empty condition, when I need to use all dataframe?

I found solutions for numeric columns, but how to work with strings?

How dynamic... if you already have code that you'd like to use such as df.str_column.str.len() > 10 - can you not just pass a dataframe that's already subsetted to myfunc... so you call it as myfunc(df[df.str_column.str.len() > 10]) ? — Jon Clements
– Jon Clements, Commented Aug 27, 2018 at 11:06
I want to do some code with different parts of dataframe, based on different conditions. You're right! It would be easier to pass a part of dataframe. — Catherine Nosova
– Catherine Nosova, Commented Aug 27, 2018 at 11:42

jezrael · Accepted Answer · 2018-08-27 10:49:59Z

1

I believe is necessary create boolean masks:

#boolean mask
cond = df.str_column.str.len()>10
#return all values
cond = [True] * len(df)

myfunc(cond)

answered Aug 27, 2018 at 10:49

jezrael

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