I want to create a new column in Pandas using a string sliced for another column in the dataframe.
For example.
Sample Value New_sample
AAB 23 A
BAB 25 B
Where New_sample is a new column formed from a simple [:1] slice of Sample
I've tried a number of things to no avail - I feel I'm missing something simple.
What's the most efficient way of doing this?
You can call the str method and apply a slice, this will be much quicker than the other method as this is vectorised (thanks @unutbu):
df['New_Sample'] = df.Sample.str[:1]
You can also call a lambda function on the df but this will be slower on larger dataframes:
In [187]:
df['New_Sample'] = df.Sample.apply(lambda x: x[:1])
df
Out[187]:
Sample Value New_Sample
0 AAB 23 A
1 BAB 25 B
Adding solution to a common variation when the slice width varies across DataFrame Rows:
#--Here i am extracting the ID part from the Email (i.e. the part before @)
#--First finding the position of @ in Email
d['pos'] = d['Email'].str.find('@')
#--Using position to slice Email using a lambda function
d['new_var'] = d.apply(lambda x: x['Email'][0:x['pos']],axis=1)
#--Imagine x['Email'] as a string on which, slicing is applied
Hope this Helps !
d['new_var'] = d.apply(lambda x: x['Email'][0:x['Email'].find('@')],axis=1)
You can also use slice() to slice string of Series as following:
df['New_sample'] = df['Sample'].str.slice(0,1)
From pandas documentation:
Series.str.slice(start=None, stop=None, step=None)
Slice substrings from each element in the Series/Index
For slicing index (if index is of type string), you can try:
df.index = df.index.str.slice(0,1)
df.somecolumn.str[0:1] and df.somecolumn.str.slice(0,1)?Adding a solution for when you want to take the second element from your pandas dataframe index, which is a tuple, and move it into its own column. Not sure if there is a shorter way to do this but this way works:
df["newcol"]=df.index
df["newcol"]=df["newcol"].apply(lambda x: x[1])
