# Calculating AF on subset of samples **URL:** \ **Category:** Hail Query & hailctl\ **Created:** [February 24, 2023, 11:30am UTC](https://discuss.hail.is/t/calculating-af-on-subset-of-samples/3134 "2023-02-24T11:30:13Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![igorm](https://avatars.discourse-cdn.com/v4/letter/i/e47774/32.png) [@igorm](https://discuss.hail.is/u/igorm)\ **Post date:** [February 24, 2023, 11:30am UTC](https://discuss.hail.is/t/calculating-af-on-subset-of-samples/3134/1 "2023-02-24T11:30:13Z")
Hi, I am trying to calculate AF on subset of samples but it is calculated all samples even though I successfully use mt.filter\_cols(). ```python # number of samples in mt len(mt.s.collect()) 7328 # number of samples in mt_case mt_case = mt.filter_cols(hl.set(sampleids).contains(mt.s)) len(mt_case.s.collect()) 32 mt_case.rows().to_pandas() 0 1:11854476 [T, G] rs1801131 -10.0 None False [0.249401] [10083, 4573] [0.6879776200873362, 0.31202237991266374] 14656 [3496, 741] ... ``` What is wrong with my code? Thanks. ---
**Author:** ![igorm](https://avatars.discourse-cdn.com/v4/letter/i/e47774/32.png) [@igorm](https://discuss.hail.is/u/igorm)\ **Post date:** [February 24, 2023, 2:03pm UTC](https://discuss.hail.is/t/calculating-af-on-subset-of-samples/3134/2 "2023-02-24T14:03:34Z")
I added variant\_qc to mt: `mt = hl.variant_qc(mt)` and then created subsets. The solution is that after creating subset I have to add variant\_qc again to the subset. `mt_case = hl.variant_qc(mt_case)` than mt\_case.rows() will only be calculated on subset of samples.