Assign oridinal number to unique data in a pandas dataframe column

user_15066374 0
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I have a dataframe like this:

ID  Time
0   100
1   100
2   200
3   200
4   500
5   500
6   890
...

I want to add a column of ordinal number based on column 'Time' in ascending order, like this:

ID  Time  Ordinal
0   100      1
1   100      1
2   200      2
3   200      2
4   500      3
5   500      3
6   890      4
...

Is there any elegant way to do this?

pandas dataframe python
2 Answers

You can try factorize

df['new'] =df.Time.factorize()[0]+1
df
Out[463]: 
   ID  Time  new
0   0   100    1
1   1   100    1
2   2   200    2
3   3   200    2
4   4   500    3
5   5   500    3
6   6   890    4
user_79645270

You could use pd.dataframe.rank:

>>> df["Ordinal"] = df["Time"].rank(method="dense")  # Optionally, add .astype(int) to cast to int
>>> df
   ID  Time  Ordinal
0   0   100      1.0
1   1   100      1.0
2   2   200      2.0
3   3   200      2.0
4   4   500      3.0
5   5   500      3.0
6   6   890      4.0
user_32810970
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