missing samples in longitudinal first-distances output

Hello!

I am trying to run longitudinal first-distances on a Jaccard distance matrix using the following command:

qiime longitudinal first-distances --i-distance-matrix DBA-core-metrics-results/jaccard_distance_matrix.qza --m-metadata-file metadatav.2.tsv --p-state-column Hour --p-individual-id-column studyID --p-replicate-handling random --o-first-distances DBA-first-distances-jacccard.qza

When I interactively explored the output artifact via qiime metadata tabulate, I noticed that samples belonging to only five of the six timepoints were present (missing the first timepoint). I get the same result when using the --p-baseline parameter, but for the sake of simplicity, I omitted it from the command above.

Attached is the initial metadata file used to execute the longitudinal first-distances command as well as the metadata-tabulated longitudinal first-distances output.

I suspect the problem lies in the initial metadata file and is user-mediated, but I have not been successful in my troubleshooting.

I appreciate your time and any suggestions!

P.S. I am currently running QIIME 2 2019.4, which was installed within a conda environment.

metadatav.2.tsv (6.4 KB) first-distances-metadata-tabulate.tsv (11.9 KB)

Hi @Lexie_Keding,

It sounds like this is working as intended! first-distances and first-differences look at change between sequential time points, and these interval changes are labeled with the second time point (I believe), so if you have a dataset like this:

SampleID timepoint subjectID
s1 1 A
s2 2 A
s3 3 A

with a distance matrix like this:

s1 s2 s3
s1 0.0 1.0 2.0
s2 1.0 0.0 1.5
s3 2.0 1.5 0.0

and run first-distances, your output will look like this:

SampleID Distance
s2 1.0
s3 1.5

where “s2” now refers to the distance between s1->s2 and “s3” refers to the distance between s2->s3. The first timepoint has been “dropped” because there is no previous time point present for measuring an interval change with first-distances.

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Hello @Nicholas_Bokulich,

That makes a lot of sense! I apologize for the naive question, but really appreciate your detailed explanation.

Thanks so much!

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