# How to check matrix length **URL:** \ **Category:** Hail Query & hailctl\ **Created:** [February 25, 2022, 10:46am UTC](https://discuss.hail.is/t/how-to-check-matrix-length/2530 "2022-02-25T10:46:59Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![annalisasnow](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.hail.is/annalisasnow/32/701_2.png) [@annalisasnow](https://discuss.hail.is/u/annalisasnow)\ **Post date:** [February 25, 2022, 10:47am UTC](https://discuss.hail.is/t/how-to-check-matrix-length/2530/1 "2022-02-25T10:47:00Z")
Good day! I am currently making requests to mtxes, these are raid reqs: ```auto mtx.filter_rows(mtx.rsid == "rs28680688").rsid.show() ``` As far as I get it, that’s a tiny mtx, which contains data with my rsid. However, some of those may be empty. Is there a built-in function to check whether the mtx is empty? Also, can I export those data to tsv or some other file? ---
**Author:** ![johnc1231](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.hail.is/johnc1231/32/286_2.png) [@johnc1231](https://discuss.hail.is/u/johnc1231)\ **Post date:** [February 25, 2022, 10:24pm UTC](https://discuss.hail.is/t/how-to-check-matrix-length/2530/2 "2022-02-25T22:24:13Z")
If you want to check how many rows after a filter, you can do: ```auto fmtx.filter_rows(mtx.rsid == "rs28680688").count_rows() ``` If there’s 0, then it’s empty. What exactly do you want to export to a TSV? Just the row data, the rows and the entries, something else? ---
**Author:** ![annalisasnow](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.hail.is/annalisasnow/32/701_2.png) [@annalisasnow](https://discuss.hail.is/u/annalisasnow)\ **Post date:** [February 26, 2022, 11:50am UTC](https://discuss.hail.is/t/how-to-check-matrix-length/2530/3 "2022-02-26T11:50:40Z")
I guess that’s the row data. I wish I could sen to tsv the results of the query: ```auto hl.export_vcf(mtx.filter_rows(mtx.rsid == searchIDorLOC[0]), vcfPathRSID) ``` That’s a tiny mtx, I currently reexport the one as a vcf. And then analyse with a different script. But I wish I could export the results (including rsid) to a tsv: ```auto +---------------+------------+------------+------------+------------+ | locus | alleles | 'HG003'.GT | 'HG004'.GT | 'HG002'.GT | +---------------+------------+------------+------------+------------+ | locus | array | call | call | call | +---------------+------------+------------+------------+------------+ | 1:736523 | ["T","C"] | 1/1 | 1/1 | 1/1 | ``` Like this table (though extended a bit). ---
**Author:** ![danking](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.hail.is/danking/32/43_2.png) [@danking](https://discuss.hail.is/u/danking)\ **Post date:** [February 27, 2022, 3:36pm UTC](https://discuss.hail.is/t/how-to-check-matrix-length/2530/4 "2022-02-27T15:36:46Z")
Hey @annalisasnow ! This is not well documented but you can export matrix table information to a TSV. This is documented under the documentation for [`Expression.export`](https://hail.is/docs/0.2/hail.expr.Expression.html#hail.expr.Expression.export). ```auto In [4]: import hail as hl ...: mt = hl.balding_nichols_model(3, 10, 100) ...: mt.GT.export('/tmp/foo.tsv') 2022-02-27 10:34:39 Hail: INFO: balding_nichols_model: generating genotypes for 3 populations, 10 samples, and 100 variants... 2022-02-27 10:34:40 Hail: INFO: Coerced sorted dataset 2022-02-27 10:34:40 Hail: INFO: merging 9 files totalling 5.4K... 2022-02-27 10:34:40 Hail: INFO: while writing: /tmp/foo.tsv merge time: 35.445ms In [5]: !head /tmp/foo.tsv locus alleles 0 1 2 3 4 5 6 7 8 9 1:1 ["A","C"] 0/0 0/0 0/1 1/1 0/1 0/0 0/1 0/1 0/1 0/1 1:2 ["A","C"] 1/1 1/1 1/1 0/1 0/1 1/1 0/1 0/1 1/1 0/1 1:3 ["A","C"] 1/1 0/0 0/1 1/1 1/1 0/0 1/1 0/0 1/1 1/1 1:4 ["A","C"] 0/1 0/0 0/1 1/1 0/0 0/1 0/1 0/1 0/1 0/0 1:5 ["A","C"] 1/1 0/0 0/0 0/0 0/0 0/0 0/1 1/1 0/0 0/1 1:6 ["A","C"] 1/1 0/1 1/1 0/1 0/0 0/1 0/1 0/0 0/0 0/0 1:7 ["A","C"] 0/1 0/0 0/0 0/1 0/1 1/1 0/1 0/1 0/0 0/0 1:8 ["A","C"] 0/0 1/1 0/1 1/1 0/1 1/1 0/1 0/1 1/1 1/1 1:9 ["A","C"] 1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1 ``` If you would like to include the RSID in the output, add the RSID to the row key: ```auto In [7]: import hail as hl ...: mt = hl.balding_nichols_model(3, 10, 100) ...: mt = mt.annotate_rows(rsid = 'abcdef123') ...: mt = mt.key_rows_by(*mt.row_key, 'rsid') ...: mt.GT.export('/tmp/foo.tsv') 2022-02-27 10:36:21 Hail: INFO: balding_nichols_model: generating genotypes for 3 populations, 10 samples, and 100 variants... 2022-02-27 10:36:22 Hail: INFO: Coerced sorted dataset 2022-02-27 10:36:22 Hail: INFO: Coerced sorted dataset 2022-02-27 10:36:22 Hail: INFO: merging 9 files totalling 6.4K... 2022-02-27 10:36:22 Hail: INFO: while writing: /tmp/foo.tsv merge time: 30.581ms In [8]: !head /tmp/foo.tsv locus alleles rsid 0 1 2 3 4 5 6 7 8 9 1:1 ["A","C"] abcdef123 0/1 0/1 0/1 1/1 1/1 0/0 0/1 0/1 0/1 1/1 1:2 ["A","C"] abcdef123 0/1 0/1 0/1 0/0 0/1 0/1 1/1 1/1 0/1 1/1 1:3 ["A","C"] abcdef123 0/0 0/0 0/0 0/1 0/1 0/1 0/0 0/1 0/1 0/0 1:4 ["A","C"] abcdef123 0/1 1/1 0/1 0/0 0/1 0/1 0/1 0/0 0/0 0/0 1:5 ["A","C"] abcdef123 1/1 0/0 1/1 0/0 0/1 1/1 0/1 0/1 0/1 0/1 1:6 ["A","C"] abcdef123 0/1 1/1 1/1 0/1 1/1 1/1 0/1 0/1 0/0 1/1 1:7 ["A","C"] abcdef123 0/0 0/1 0/0 0/1 0/0 0/0 0/0 0/0 0/0 0/0 1:8 ["A","C"] abcdef123 1/1 1/1 1/1 1/1 1/1 1/1 1/1 0/1 0/1 1/1 1:9 ["A","C"] abcdef123 1/1 0/1 1/1 0/1 1/1 1/1 1/1 1/1 0/1 1/1 ```