Panda .loc or .iloc to select the columns from a dataset

Question

I have been trying to select a particular set of columns from a dataset for all the rows. I tried something like below.

train_features = train_df.loc[,[0,4,5         


        

Answer 1

You can access the column values via the the underlying numpy array

Consider the dataframe df

df = pd.DataFrame(np.random.randint(10, size=(5, 20)))
df

You can slice the underlying array

slc = [0,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]
df.values[:, slc]

array([[1, 3, 9, 8, 3, 2, 1, 6, 6, 0, 3, 9, 8, 5, 9, 9],
       [8, 0, 2, 3, 7, 8, 9, 2, 7, 2, 1, 3, 2, 5, 4, 9],
       [1, 1, 9, 3, 5, 8, 8, 8, 8, 4, 8, 0, 5, 4, 9, 0],
       [6, 3, 1, 8, 0, 3, 7, 9, 9, 0, 9, 7, 6, 1, 4, 8],
       [3, 2, 3, 3, 9, 8, 3, 8, 3, 4, 1, 6, 4, 1, 6, 4]])

Or you can reconstruct a new dataframe from this slice

pd.DataFrame(df.values[:, slc], df.index, df.columns[slc])

This is not as clean and intuitive as

df.iloc[:, slc]

You could also use slc to slice the df.columns object and pass that to df.loc

df.loc[:, df.columns[slc]]

Answer 2

If need select by positions use iloc:

train_features = train_df.iloc[:, [0,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]]
print (train_features)
   age  default  housing  loan  equities  contact  duration  campaign  pdays  \
0   56        1        1     1         1        0       261         1    999   
1   37        1        0     1         1        0       226         1    999   
2   56        1        1     0         1        0       307         1    999   

   previous  poutcome  emp.var.rate  cons.price.idx  cons.conf.idx  euribor3m  \
0         0         2           1.1          93.994          -36.4   3.299552   
1         0         2           1.1          93.994          -36.4   0.743751   
2         0         2           1.1          93.994          -36.4   1.282652   

   nr.employed  
0         5191  
1         5191  
2         5191  

Another solution is drop unnecessary columns:

cols= ['job','marital','education','y']
train_features = train_df.drop(cols, axis=1)
print (train_features)
   age  default  housing  loan  equities  contact  duration  campaign  pdays  \
0   56        1        1     1         1        0       261         1    999   
1   37        1        0     1         1        0       226         1    999   
2   56        1        1     0         1        0       307         1    999   

   previous  poutcome  emp.var.rate  cons.price.idx  cons.conf.idx  euribor3m  \
0         0         2           1.1          93.994          -36.4   3.299552   
1         0         2           1.1          93.994          -36.4   0.743751   
2         0         2           1.1          93.994          -36.4   1.282652   

   nr.employed  
0         5191  
1         5191  
2         5191