CODEWITHSUNDEEP
pythonpandas
LetsPlayYahtzee
LetsPlayYahtzee

Reputation: 7581

Apply condition on pandas columns to create a boolen indexing array

I want to drop specific rows from a pandas dataframe. Usually you can do that using something like

df[df['some_column'] != 1234]

What df['some_column'] != 1234 does is creating an indexing array that is indexing the new df, thus letting only rows with value True to be present.

But in some cases, like mine, I don't see how I can express the condition in such a way, and iterating over pandas rows is way too slow to be considered a viable option.

To be more specific, I want to drop all rows where the value of a column is also a key in a dictionary, in a similar manner with the example above.

In a perfect world I would consider something like

df[df['some_column'] not in my_dict.keys()]

Which is obviously not working. Any suggestions?

Upvotes: 5

Views: 416

Answers (3)

Saurav Gupta
Saurav Gupta

Reputation: 535

What you're looking for is isin()

import pandas as pd

df = pd.DataFrame([[1, 2], [1, 3], [4, 6],[5,7],[8,9]], columns=['A', 'B'])
In[9]: df
Out[9]: df
   A  B
0  1  2
1  1  3
2  4  6
3  5  7
4  8  9
mydict = {1:'A',8:'B'}
df[df['A'].isin(mydict.keys())]
Out[11]: 
   A  B
0  1  2
1  1  3
4  8  9

Upvotes: 2

Jose Raul Barreras
Jose Raul Barreras

Reputation: 859

You can use the function isin() to select rows whose column value is in an iterable.

Using lists:

my_list = ['my', 'own', 'data']
df.loc[df['column'].isin (my_list)]

Using dicts:

my_dict = {'key1':'Some value'}
df.loc[df['column'].isin (my_dict.keys())]

Upvotes: 1

Nickil Maveli
Nickil Maveli

Reputation: 29711

You could use query for this purpose:

df.query('some_column != list(my_dict.keys()')

Upvotes: 1

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