issues: 174390114
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id | node_id | number | title | user | state | locked | assignee | milestone | comments | created_at | updated_at | closed_at | author_association | active_lock_reason | draft | pull_request | body | reactions | performed_via_github_app | state_reason | repo | type |
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174390114 | MDU6SXNzdWUxNzQzOTAxMTQ= | 995 | xarray slicing is very slow, and reading time differs a lot between variables. | 7747527 | closed | 0 | 2 | 2016-08-31T22:02:42Z | 2016-09-01T03:24:49Z | 2016-09-01T03:17:52Z | NONE | Hi everyone, I've been working on calculating ocean heat transport across a prescribed section. Therefore, I need to calculate the V*T (velocity times T) on the grid points along that section. Xarray has been the my favorite tool, ever since the day it was still xray. In my code, there is a loop (looping through grid points along the line) that determine if I need to use U (zonal velocity) or V (meridional velocity). Then times it by the temperature on that location, which is full depth. VVEL, UVEL and TEMP have structure like this (time: 1, z_t: 42, lat: 1800, lon: 3600)
The weird thing is, for VVEL and UVEL, it takes about 5sec with slicing, about 2 sec without slicing, but for TEMP, it only needs 6ms. This then leads to another issue, within the loop, I need to extract a vertical column of temperature,
This line drags everything down, it takes about 4sec... but this is repeated for each loop (rouhgly 300 times).
I found out that, removing What's more interesting is that, in the loop, I also have this line
Which has the exact same structure as the line I used to call the column values of temperature. But this line only needs about 1ms, with and without calling Could someone please explain how is this possible? All these variables are from the same netcdf file. And I called them in the exact same way. Also, why is slicing takes even longer then loading in the full field? Any suggestion I can circumvent this bottleneck? Thank you. |
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completed | 13221727 | issue |