Condition from a string to select dataframe rows

Question

I have a dataframe like this:

data = [[1, 0, 1],
        [1, 1, 1],
        [0, 0, 1]]

df = pd.DataFrame(data=data, columns=['col1', 'col2', 'col3'])

and from a string like this:

cond_str = ['col1 >= 1', 'col3 >= 1']

and I would like to achieve this:

df.loc[(df['col1'] >= 1) & (df['col3'] >= 1)]

Is there any simple way to do this or do I have to write my own parsing function for this?

You want ti divide your cond_str list in df.loc[(df['col1'] >= 1) & (df['col3'] >= 1)] with some modification? — Vishal Upadhyay
– Vishal Upadhyay, Commented May 1, 2020 at 14:55

jmkjaer · Accepted Answer · 2020-05-01 14:57:40Z

5

You can use query:

df.query("&".join(cond_str))

which results in

   col1  col2  col3
0     1     0     1
1     1     1     1

answered May 1, 2020 at 14:57

jmkjaer

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2 Comments

yatu Over a year ago

Nice! For some reason I assumed bitwise operators wouldn't work with eval or query, TIL they do :)

jmkjaer Over a year ago

@yatu I thought the same the first time I encountered this, but I very much like it. :)

Saurabh Kansal · Accepted Answer · 2020-05-01 15:03:21Z

0

you can use eval of python to evaluate a string expression. e.g. for your case

df = pd.DataFrame(data=data, columns=['col1', 'col2', 'col3'])
print(df)

    col1  col2  col3
0     1     0     1
1     1     1     1
2     0     0     1

cond_str_list = ['col1 >= 1', 'col3 >= 1']

cond_str = ' & '.join(['(df.'+i+')' for i in  cond_str_list])

print(cond_str)

df = df[eval(cond_str)]

print(df)

    col1  col2  col3
0     1     0     1
1     1     1     1

answered May 1, 2020 at 15:03

Saurabh Kansal

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