# Variant qc AF field index meaning

**URL:** <https://discuss.hail.is/t/variant-qc-af-field-index-meaning/953>\
**Category:** Hail Query & hailctl\
**Created:** [May 8, 2019, 3:19am UTC](https://discuss.hail.is/t/variant-qc-af-field-index-meaning/953 "2019-05-08T03:19:17Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![njbernstein](https://avatars.discourse-cdn.com/v4/letter/n/e9bcb4/32.png) [@njbernstein](https://discuss.hail.is/u/njbernstein)\
**Post date:** [March 19, 2020, 8:24pm UTC](https://discuss.hail.is/t/variant-qc-af-field-index-meaning/953/3 "2020-03-19T20:24:04Z")

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@tpoterba how would one run something similar but when AF isn’t defined for every entry:

I tried:

```auto
chip_vars_mt = chip_vars_mt.annotate_cols(test = 
                                          hl.agg.filter(hl.is_defined(chip_vars_mt.AF), hl.agg.mean(chip_vars_mt.AF[1])))
chip_vars_mt.col.test.show(1)

```

But get the following error:

```auto
Hail version: 0.2.34-914bd8a10ca2
Error summary: HailException: array index out of bounds: index=1, length=1
----------
Python traceback:
  File "<ipython-input-131-84c67a4862a4>", line 2, in <module>
    hl.agg.filter(hl.is_defined(chip_vars_mt.AF), hl.agg.mean(chip_vars_mt.AF[1])))

```

Thoughts?

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_[View the full topic](https://discuss.hail.is/t/variant-qc-af-field-index-meaning/953)._