Adding value 0 to existing column based on comma

Question

I have a DataFrame that looks like below:

name price
x    ,12
y    ,9
z    10,25

I have to add "0" before the comma (unless there is already a number before the comma, in that case it can't be changed) so DataFrame should looks like below:

name price
x    0,12
y    0,9
z    10,25

Do you have any ideas?

Answer 1

Assuming you are working with strings and not numbers, this does the trick for me:

df["price"] = df["price"].where(~df["price"].str.startswith(","), "0"+df["price"])

Here is an example

df = pd.DataFrame([["x",",12"],["y",",3"],["z","5"],["o","1,2"]], columns=["name","price"])
print("input:", df)
df["price"] = df["price"].where(~df["price"].str.startswith(","), "0"+df["price"])
print("output:", df)

yields:

input:   name price
0    x   ,12
1    y    ,3
2    z     5
3    o   1,2
output:   name price
0    x  0,12
1    y   0,3
2    z     5
3    o   1,2