General
PromptBeginner5 minmarkdownQuality: 28
- Returns columns named after the grouping variables
with result column keeping the original name.
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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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General
PromptBeginner5 minmarkdownQuality: 28
- cbind(NULL) returns NULL (not a matrix). For consistency
rbind(NULL) also returns NULL.
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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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General
PromptBeginner5 minmarkdownQuality: 24
- Supports formula syntax: `split(df
~ Month)`.
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General
PromptBeginner5 minmarkdownQuality: 28
- ... args to FUN are not divided into cells — they apply globally
so FUN should not expect additional args with same length as X.
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General
PromptBeginner5 minmarkdownQuality: 24
- by = 0 or by = row.names merges on row names
adding a Row.names column.
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General
PromptBeginner5 minmarkdownQuality: 24
- ... args cannot share names with X
MARGIN
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General
PromptBeginner5 minmarkdownQuality: 24
- sapply can return a vector
matrix
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General
PromptBeginner5 minmarkdownQuality: 24
- Factors
raw vectors
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General
PromptBeginner5 minmarkdownQuality: 24
- Return value orientation is transposed: if FUN returns length-n vector
result has dim `c(n
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Coding & Debugging
PromptBeginner5 minmarkdownQuality: 28
- Factor indexing: x[f] uses integer codes of factor f
not its character labels. Use x[as.character(f)] for label-based indexing.
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General
PromptBeginner5 minmarkdownQuality: 24
- `m[j = 2
i = 1] is m[2
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General
PromptBeginner5 minmarkdownQuality: 24
Non-obvious behaviors
gotchas
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General
PromptBeginner5 minmarkdownQuality: 28
- stl requires s.window (seasonal window) — must be specified
no default. s.window = periodic assumes fixed seasonality.
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General
PromptBeginner5 minmarkdownQuality: 24
- stl result components: $time.series matrix with columns seasonal
trend
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General
PromptBeginner5 minmarkdownQuality: 24
- decompose: simpler than stl
uses moving averages. type = additive or multiplicative.
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General
PromptBeginner5 minmarkdownQuality: 24
- `arima(x
order = c(p
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