Change isel to sel to fix compute_Sv

[lsetiawan]

This PR adress #824 (comment) where idxmin is actually xarray data array object not integers, so isel doesn't work.

[codecov-commenter]

Codecov Report

Merging #828 (c1eeac6) into dev (76e7d28) will increase coverage by 9.72%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #828      +/-   ##
==========================================
+ Coverage   83.09%   92.81%   +9.72%     
==========================================
  Files          52        5      -47     
  Lines        4915      543    -4372     
==========================================
- Hits         4084      504    -3580     
+ Misses        831       39     -792     

Flag	Coverage Δ
unittests	92.81% <100.00%> (+9.72%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
echopype/calibrate/calibrate_ek.py	93.61% <100.00%> (-0.71%)	⬇️
echopype/calibrate/env_params.py	89.47% <0.00%> (-3.51%)	⬇️
echopype/convert/parse_ek60.py
echopype/convert/set_groups_azfp.py
echopype/convert/parsed_to_zarr_ek60.py
echopype/echodata/widgets/utils.py
echopype/echodata/__init__.py
echopype/convert/utils/ek_raw_io.py
echopype/echodata/api.py
... and 40 more

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[b-reyes]

@lsetiawan from my understanding, we should replace all isel operations on something that could potentially be a Dask array. Searching through just the calibrate folder, I found a couple of other occurrences of isel. Could you look into the following occurrences and determine if they also need to be changed?

• In calibrate_ek.py Line 852: return out.isel(beam=0).drop("beam")
• In env_params.py Line 146: extrap = extrap.isel(**extrap_unique_idx)
• In env_params.py Line 152: interp = interp.isel(**interp_unique_idx)

[b-reyes]

I looked into this change and everything looks good.

[lsetiawan]

In calibrate_ek.py Line 852: return out.isel(beam=0).drop("beam")

For this one, the value is clearly 0 so isel is appropriate, I'll take look at the other files.

[lsetiawan]

In env_params.py Line 146: extrap = extrap.isel(**extrap_unique_idx)
In env_params.py Line 152: interp = interp.isel(**interp_unique_idx)

For these two, I'm not sure how to check for these, I'm not familiar enough with the env_params module. @leewujung I need your guidance on this. Thanks.

[b-reyes]

For this one, the value is clearly 0 so isel is appropriate, I'll take look at the other files.

Yes, I understand that isel would be appropriate here. However, from my understanding, if out is referring to a Dask array then out.isel will not work. Here, I think we are just trying to drop any lingering beam dimension. So, one could just find the first value in the beam dimension and use this value to replace isel with sel.

[b-reyes]

Everything looks good!