Slow .SD[.N] compare to last(.SD) with groupby
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 35/100
- Issue type
- Bug
- Clarity
- Mostly clear
- Activity status
- Stale
- Tech stack
- r
- Domain
- data, performance
Research direction
Start by reproducing the grouped expressions DT[,.SD[.N], by=col] and DT[,.last(.SD), by=col] on the large data described, then compare them with the corresponding .SD[1] and first(.SD) cases. Use the reported performance difference as the investigation target; done means its cause is explained and any confirmed regression is addressed without worsening the matching first-row case.
Written by the indexing model from the issue text.
Description
I noticed there is significant speed difference between
DT[,.SD[.N], by=col] and
DT[,.last(.SD), by=col]
for relatively large data (10 * 1.8M rows).
DT[,.SD[1],by=col] and DT[,first(.SD), by=col] did not show difference in performance, however.
- Dominant language
- R
- Stars
- 3.9k
- Forks
- 1.1k
- Avg merge
- 14h 4m
- Merged PRs (30d)
- 4
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
More from Rdatatable/data.table
-
as.data.table() recurses without end on a survival::Surv object (or any data.frame carrying one) Open
Difficulty 2/5 1-3 hours Newbie friendliness 88/100
Rdatatable/data.table#7887 ·
-
consistency tests
Difficulty 2/5 1-3 hours Newbie friendliness 68/100
Rdatatable/data.table#7853 · 3 comments ·
-
internals
Difficulty 2/5 1-3 hours Newbie friendliness 65/100
Rdatatable/data.table#6938 · 1 comment ·
-
encoding fread
Difficulty 2/5 1-3 hours Newbie friendliness 65/100
Rdatatable/data.table#5179 · 8 comments ·
-
documentation programming
Difficulty 2/5 1-3 hours Newbie friendliness 68/100
Rdatatable/data.table#3199 · 3 comments ·
All issues in Rdatatable/data.table
Similar issues
-
Difficulty 2/5 1-3 hours Newbie friendliness 82/100
r-lib/pkgdepends#485 · 3 comments ·
-
Difficulty 1/5 Under an hour Newbie friendliness 92/100
-
beginners blocker
Difficulty 2/5 1-3 hours Newbie friendliness 78/100
-
enviPathR OpenBuild Error Build OK Build Warning policies-accepted pre-review precheck-passed
Difficulty 1/5 Under an hour Newbie friendliness 84/100
Bioconductor/BiocContributions#207 · 6 comments ·
-
Difficulty 2/5 1-3 hours Newbie friendliness 74/100
datacarpentry/semester-biology#1255 ·