Get values from column that appear more than X times (without pandas or external libraries) I have a .csv file that contains a row with various loan IDs. I would like to be able to output the IDs that occur 6 or more times.

CUST_ID,PROD,BAL,PER
1151612518-107,1151612518-107c,780.1,4
1151612518-1049,1151612518-1049a,344.72,2
1151612518-813,1151612518-813a,1376.1,6
1151612518-427,1151612518-427a,913.51,4
1151612518-1056,1151612518-1056a,1851.49,7


The data is in this format and I would like to have a way to analyze the first column and output every CUST_ID that occurs 6 or more times.
The "no pandas or other external libraries" instruction was included in the homework question? ;-)

You need a group-by the CUST_ID and then select on the count in each group. 

Your question doesn't specify, but you tag with Python. Otherwise I would say to load the data into an SQL database or use the great CSV toolkit.

If you need to implement it using Python, the group-by is done by sorting on CUST_ID, and then going through the sorted data (with a for-loop, for example), counting the number of repeated CUST_ID's. When the CUST_ID changes, you check how often you have seen this CUST_ID. If greater than X, then you output this CUST_ID. Otherwise, reset your counter.