Pandas extract data from column

Question

I have a dataframe like this

import pandas as pd
d={'x':[8,5,6,7],
   'cord':['(3,0)','(2,0)','(6,0)','(1,0)']}
df=pd.DataFrame.from_dict(d)

I would like to create df['y'] which will have the first 'cord' value and shift to get index value.

    cord  x  y
0  (3,0)  8  1     #Index 3, First value in (1,0)
1  (2,0)  5  6     #Index 2, First value in (6,0)
2  (6,0)  6  NaN   #Index 6, does not exist, NaN
3  (1,0)  7  2     #Index 1, First value (1,0)

Answer 1

Make a separate column, which is the first element of cord

df['cord1'] = df.cord.map( lambda x: x.split(',')[0].split('(')[-1]).map(int)
df
#    cord  x  cord1
#0  (3,0)  8      3
#1  (2,0)  5      2
#2  (6,0)  6      6
#3  (1,0)  7      1

This might look confusing, but it simply splits the string '(a,b)' twice, first on ',' , and then on '(' . Finally, it casts the remaining string , 'a' , to an integer.

Now use the cord1 column to make the y column

df['y'] =  df.cord1[ df.cord1.values].values

being careful to pass the values. Now drop the cord1 column

df.drop( labels='cord1', axis=1, inplace=True)

#df
#    cord  x   y
#0  (3,0)  8   1
#1  (2,0)  5   6
#2  (6,0)  6 NaN
#3  (1,0)  7   2