Pad the start of values with zeros in polars

zfill

You have a shop and want your receipt numbers to have four digits instead of just one. So rather than receipt “No. 1”, you want receipt “No. 0001”. Below is a dataframe showing customers and their receipt numbers.

shape: (4, 2)

Customer	Receipt No
str	i64
"Serena"	1
"Blair"	2
"Dan"	21
"Vanessa"	153

Pad with zeros

To add zeros at the start of values in Receipt No, you first need to convert the column’s data type to string (text) and then use the Polars expression zfill, like this:

(df
 .with_columns(pl.col('Receipt No').cast(pl.String).str.zfill(length=4))
 )

shape: (4, 2)

Customer	Receipt No
str	str
"Serena"	"0001"
"Blair"	"0002"
"Dan"	"0021"
"Vanessa"	"0153"

Note

Setting length=4 means the final value will have 4 digits. It does not mean the number of zeros to add.

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