How do I iterate through and Pandas data frame column and concatenate a number to a string?

I am attempting to iterate through a column and add a number based on the count of instances the duplicate value takes place. This will give me a unique value in my dataset. The data I have is below:

    FY  group   item    concat
0   2015    GROUP_A 1   2015-GROUP_A-1
1   2015    GROUP_A 1   2015-GROUP_A-1
2   2015    GROUP_A 1   2015-GROUP_A-1
3   2015    GROUP_A 10  2015-GROUP_A-10
4   2015    GROUP_A 7   2015-GROUP_A-7
5   2015    GROUP_B 23  2015-GROUP_B-23
6   2015    GROUP_B 23  2015-GROUP_B-23
7   2015    GROUP_B 23  2015-GROUP_B-23
8   2015    GROUP_B 23  2015-GROUP_B-23
9   2015    GROUP_B 21  2015-GROUP_B-2

I am looking to return something like this:

FY  group   item    concat  uid
2015    GROUP_A 1   2015-GROUP_A-1  2015-GROUP_A-1-1
2015    GROUP_A 1   2015-GROUP_A-1  2015-GROUP_A-1-2
2015    GROUP_A 1   2015-GROUP_A-1  2015-GROUP_A-1-3
2015    GROUP_A 10  2015-GROUP_A-10 2015-GROUP_A-10-1
2015    GROUP_A 7   2015-GROUP_A-7  2015-GROUP_A-7-1
2015    GROUP_B 23  2015-GROUP_B-23 2015-GROUP_B-23-1
2015    GROUP_B 23  2015-GROUP_B-23 2015-GROUP_B-23-2
2015    GROUP_B 23  2015-GROUP_B-23 2015-GROUP_B-23-3
2015    GROUP_B 23  2015-GROUP_B-23 2015-GROUP_B-23-4
2015    GROUP_B 21  2015-GROUP_B-21 2015-GROUP_B-21-1

I greatly appreciate any help!

>Solution :

You could count the number of consecutive values in each concat group, adding 1 to each to offset the zero indexing

df['uid'] = df['concat'] + '-' + (df.groupby('concat').cumcount()+1).astype(str)