CODEWITHSUNDEEP
pandas
TimGJ
TimGJ

Reputation: 1654

Returning column names matching criteria in pandas

I have a pandas dataframe which is a square grid of boolean values with the index and columns being the names of 628 electoral constituencies which have neighbours. e.g. 

In[18]: adjacents.index
Out[18]: 
Index(['Aberavon', 'Aberconwy', 'Aberdeen North', 'Aberdeen South',
       'Aberdeenshire West & Kincardine', 'Airdrie & Shotts', 'Aldershot',
       'Aldridge-Brownhills', 'Altrincham & Sale West', 'Alyn & Deeside',
       ...
       'Wrekin, The', 'Wrexham', 'Wycombe', 'Wyre & Preston North',
       'Wyre Forest', 'Wythenshawe & Sale East', 'Yeovil', 'York Central',
       'York Outer', 'Yorkshire East'],
      dtype='object', length=628)

In[19]: adjacents.columns
Out[19]: 
Index(['Aberavon', 'Aberconwy', 'Aberdeen North', 'Aberdeen South',
       'Aberdeenshire West & Kincardine', 'Airdrie & Shotts', 'Aldershot',
       'Aldridge-Brownhills', 'Altrincham & Sale West', 'Alyn & Deeside',
       ...
       'Wrekin, The', 'Wrexham', 'Wycombe', 'Wyre & Preston North',
       'Wyre Forest', 'Wythenshawe & Sale East', 'Yeovil', 'York Central',
       'York Outer', 'Yorkshire East'],
      dtype='object', length=628)

So, Manchester Central constiuency is adjacent to Manchester Gorton, but not Manchester Withington.

In[20]: adjacents['Manchester Central']['Manchester Withington']
Out[20]: False

In[21]: adjacents['Manchester Central']['Manchester Gorton']
Out[21]: True

What's the best way to return the column names for all columns in a row which are True? (I think it might be something to do with np.argmax() but can't quite figure it out.)

Upvotes: 0

Views: 80

Answers (1)

Shovalt
Shovalt

Reputation: 6766

Well, you could do that, but since your matrix seems to be symmetric you'd be better off finding the row names instead, since this is much simpler:

adjacents[adjacents['Manchester Central']].index

BTW - when accessing an exact location in the table, it is better practice to use loc:

adjacents.loc['Manchester Central', 'Manchester Gorton']

Upvotes: 1

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