How to construct condition in a loop in Python?

Question

I want to construct a condition for my dataframe in a function by iterating through the given dictionary dict.

def get_condition(dataframe, dict={'col1':val1, 'col2':val2, 'col3':val3})":

     condition = ...          

     return condition

Expected output

condition = (dataframe['col1']==val1) & (dataframe['col2']==val2) & (dataframe['col3']==val3)

How to do this?

Do you want to build a string, or to actually execute and resolve this condition ? — NanoPish
– NanoPish, Commented Jul 26, 2018 at 13:37
At the end I want to have a dataframe_new = dataframe[condition] . But I want construct this condition first iteratively using a function. — Yulia
– Yulia, Commented Jul 26, 2018 at 13:41
I think stroring the strings and then using eval() would work, if I understood what you want ? But it sounds like a code smell ? — NanoPish
– NanoPish, Commented Jul 26, 2018 at 13:43
See answer. In reference to your original code, beware of mutable default arguments. Also, by using dict as the variable name for your dictionary, you're overwriting the builtin dict type/function, which should generally be avoided if possible. — sundance
– sundance, Commented Jul 26, 2018 at 13:56

sundance · Accepted Answer · 2018-07-26 13:52:30Z

3

def get_condition(df, d):
    d = list(d.items())

    first_col, first_val = d[0]
    cond = df[first_col] == first_val
    for col, val in d[1:]:
        cond &= df[col] == val

    return cond

answered Jul 26, 2018 at 13:52

sundance

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Comments

Alex G · Accepted Answer · 2018-07-26 14:05:27Z

2

Not sure, if you want to create a boolean filter.

def get_condition(dataframe, dictionary):
    # create series with all values set to true
    condition = pd.Series([True] * len(dataframe))

    for k, v in dictionary.items():
        condition &= dataframe[k] == v
    return condition

answered Jul 26, 2018 at 14:05

Alex G

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