# Cannot combine expressions from different source objects

**URL:** <https://discuss.hail.is/t/cannot-combine-expressions-from-different-source-objects/1220>\
**Category:** Hail Query & hailctl\
**Created:** [December 16, 2019, 9:18pm UTC](https://discuss.hail.is/t/cannot-combine-expressions-from-different-source-objects/1220 "2019-12-16T21:18:33Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![ch-kr](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.hail.is/ch-kr/32/317_2.png) [@ch-kr](https://discuss.hail.is/u/ch-kr)\
**Post date:** [December 16, 2019, 9:18pm UTC](https://discuss.hail.is/t/cannot-combine-expressions-from-different-source-objects/1220/1 "2019-12-16T21:18:34Z")

</div>

I’m running into this error:

```auto
hail.expr.expressions.base_expression.ExpressionException: Cannot combine expressions from different source objects.
    Found fields from 2 objects:
        <hail.table.Table object at 0x7f5ff943be10>: ['sample_qc', 'sample_qc', 'sample_qc', 'sample_qc', 'sample_qc', 'sample_qc', 'qc_pop']
        <hail.table.Table object at 0x7f5ff943b710>: ['batch.c']

```

while running this code:

```auto
if not args.skip_platform_filter:
        logger.info('Annotating platform assignments...')
        #platform_ht = hl.read_table(platform_pca_results_ht_path(data_source, freeze))
        #sample_qc_ht = sample_qc_ht.annotate(qc_platform=platform_ht[sample_qc_ht.key].qc_platform)
        sample_map_ht = hl.read_table(array_sample_map_ht(data_source, freeze))
        sample_map = hl.import_table(array_sample_map(freeze), delimiter=',', quote='"')
        sample_map = sample_map.key_by(s=sample_map.eid_26041)
        sample_qc_ht = sample_qc_ht.annotate(**sample_map_ht[sample_qc_ht.s])
        sample_qc_ht = sample_qc_ht.annotate(**sample_map[sample_qc_ht.ukbb_app_26041_id])
        strata['qc_platform'] = sample_qc_ht['batch.c']
        #strata['qc_platform'] = sample_qc_ht.qc_platform
if not args.skip_population_filter:
        logger.info('Annotating population assignments...')
        pop_ht = hl.read_table(ancestry_hybrid_ht_path(data_source, freeze))
        sample_qc_ht = sample_qc_ht.annotate(qc_pop=pop_ht[sample_qc_ht.key][pop_assignment_method])
        strata['qc_pop'] = sample_qc_ht.qc_pop
else:
        pop_assignment_method = None
# Make qc_metrics a dict (needs to be dict for compute_stratified_metrics_filte
metrics = args.filtering_qc_metrics.split(",")
qc_metrics = {}
for m in metrics:
        qc_metrics[m] = sample_qc_ht.sample_qc[f'{m}']

# For each platform and population, aggregate sample QC metrics and calculate the MAD/mean/stdev
logger.info('Flagging samples failing pop/platform-specific sample qc thresholds...')
print(strata)
print(qc_metrics)
pop_platform_filter_ht = compute_stratified_metrics_filter(
        sample_qc_ht,
        qc_metrics,
        strata
    )

```

`compute_stratified_metrics_filter`: [https://github.com/macarthur-lab/gnomad\_hail/blob/master/utils/sample\_qc.py#L654](https://github.com/macarthur-lab/gnomad_hail/blob/master/utils/sample_qc.py#L654)

Why is it saying the tables are different? The numbers it’s outputting are the same. Also, changing the code to be

```auto
if not args.skip_platform_filter:
        logger.info('Annotating platform assignments...')
        #platform_ht = hl.read_table(platform_pca_results_ht_path(data_source, freeze))
        #sample_qc_ht = sample_qc_ht.annotate(qc_platform=platform_ht[sample_qc_ht.key].qc_platform)
        sample_map_ht = hl.read_table(array_sample_map_ht(data_source, freeze))
        sample_map = hl.import_table(array_sample_map(freeze), delimiter=',', quote='"')
        sample_map = sample_map.key_by(s=sample_map.eid_26041)
        sample_qc_ht = sample_qc_ht.annotate(**sample_map_ht[sample_qc_ht.s])
        sample_qc_ht = sample_qc_ht.annotate(**sample_map[sample_qc_ht.ukbb_app_26041_id])
        #strata['qc_platform'] = sample_qc_ht['batch.c']
        #strata['qc_platform'] = sample_qc_ht.qc_platform
if not args.skip_population_filter:
        logger.info('Annotating population assignments...')
        pop_ht = hl.read_table(ancestry_hybrid_ht_path(data_source, freeze))
        sample_qc_ht = sample_qc_ht.annotate(qc_pop=pop_ht[sample_qc_ht.key][pop_assignment_method])
        strata['qc_pop'] = sample_qc_ht.qc_pop
        strata['qc_platform'] = sample_qc_ht['batch.c']
else:
        pop_assignment_method = None

```

fixes the error.

---

<div class="post-metadata">

**Author:** ![ch-kr](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.hail.is/ch-kr/32/317_2.png) [@ch-kr](https://discuss.hail.is/u/ch-kr)\
**Post date:** [December 16, 2019, 10:12pm UTC](https://discuss.hail.is/t/cannot-combine-expressions-from-different-source-objects/1220/2 "2019-12-16T22:12:24Z")

</div>

Nevermind, I think I’ve figured this out – thanks!