Add leading zeros based on condition in python

Question

I have a dataframe with 5 million rows. Let's say the dataframe looked like below:

>>> df = pd.DataFrame(data={"Random": "86 7639103627 96 32 1469476501".split()})
>>> df
       Random
0          86
1  7639103627
2          96
3          32
4  1469476501

Note that the Random column is stored as a string.

If the number in column Random has fewer than 9 digits, I want to add leading zeros to make it 9 digits. If the number has 9 or more digits, I want to add leading zeros to make it 20 digits.

what I have done is this:

for i in range(0,len(df['Random'])):
      if len(df['Random'][i]) < 9:
          df['Random'][i]=df['Random'][i].zfill(9)
      else:
           df['Random'][i]=df['Random'][i].zfill(20)

Since the number of rows is over 5 million, this process takes a lot of time! (performance was 5it/sec. Tested using tqdm, estimated time of completion was in days!).

Is there an easier and faster way of performing this task?

Answer 1

Let us do np.where combine with zfill, alternative you can check with str.pad

df.Random=np.where(df.Random.str.len()<9,df.Random.str.zfill(9),df.Random.str.zfill(20))
df
Out[9]: 
                 Random
0             000000086
1  00000000007639103627
2             000000096
3             000000032
4  00000000001469476501