General
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- POSIXlt: list with components $sec
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General
PromptBeginner5 minmarkdownQuality: 24
Non-obvious behaviors
gotchas
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General
PromptBeginner5 minmarkdownQuality: 24
- `format(date
%Y)` for year
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General
PromptBeginner5 minmarkdownQuality: 24
- `seq.Date(from
to
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General
PromptBeginner5 minmarkdownQuality: 24
- Returns a permutation vector of indices
not the sorted values. Use x[order(x)] to sort.
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General
PromptBeginner5 minmarkdownQuality: 28
- For character sorting
depends on locale. Use method = radix for locale-independent fast sorting.
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General
PromptBeginner5 minmarkdownQuality: 24
- Default is ascending; use -x for descending numeric
or decreasing = TRUE.
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Data
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- If FUN returns multiple values
result column is a matrix column inside the data frame.
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General
PromptBeginner5 minmarkdownQuality: 24
- Works on multiple arguments (e.g.
`complete.cases(x
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General
PromptBeginner5 minmarkdownQuality: 28
- Returns columns named after the grouping variables
with result column keeping the original name.
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Data
PromptBeginner5 minmarkdownQuality: 24
- Formula interface (`aggregate(y ~ x
data
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General
PromptBeginner5 minmarkdownQuality: 24
- c() on factors unions level sets (since R 4.1.0)
but earlier versions converted to integer.
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General
PromptBeginner5 minmarkdownQuality: 24
- Levels are sorted by default
but sort order is locale-dependent at creation time.
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General
PromptBeginner5 minmarkdownQuality: 28
- Only == and != work between factors; factors must have identical level sets. Ordered factors suppo...
.
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General
PromptBeginner5 minmarkdownQuality: 28
- Duplicate column names allowed only with check.names = FALSE
but many operations will de-dup them silently.
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Coding & Debugging
PromptBeginner5 minmarkdownQuality: 28
- as.numeric(f) returns integer codes
not original values. Use as.numeric(levels(f))[f] or as.numeric(as.character(f)).
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General
PromptBeginner5 minmarkdownQuality: 28
- duplicated marks the second and later occurrences as TRUE
not the first. Use fromLast = TRUE to reverse.
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General
PromptBeginner5 minmarkdownQuality: 28
- Atomic vectors recycle to match longest column
but only if exact multiple. Protect with I() to prevent conversion.
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Data
PromptBeginner5 minmarkdownQuality: 24
- For data frames
operates on whole rows. For lists
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General
PromptBeginner5 minmarkdownQuality: 28
- cbind(NULL) returns NULL (not a matrix). For consistency
rbind(NULL) also returns NULL.
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Data
PromptBeginner5 minmarkdownQuality: 28
- Result is always an array (even 1D)
class table. Convert to data frame with as.data.frame(tbl).
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Data
PromptBeginner5 minmarkdownQuality: 24
- rbind on data frames matches columns by name
not position. Missing columns get NA.
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General
PromptBeginner5 minmarkdownQuality: 28
- If f is a list of factors
interaction is used; levels containing . can cause unexpected splits unless sep is changed.
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Data
PromptBeginner5 minmarkdownQuality: 28
- cbind on data frames calls data.frame(...)
not cbind.matrix. Mixing matrices and data frames can give unexpected results.
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