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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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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Data
PromptBeginner5 minmarkdownQuality: 28
- Default by is `intersect(names(x)
names(y))` — can silently merge on unintended columns if data frames share column names.
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Data
PromptBeginner5 minmarkdownQuality: 28
- Returns an array (not a data frame). Class info on return values is discarded (e.g.
Date objects become numeric).
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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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Data
PromptBeginner5 minmarkdownQuality: 28
- On a data frame
apply coerces to matrix via as.matrix first — mixed types become character.
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Data
PromptBeginner5 minmarkdownQuality: 28
- subset argument uses non-standard evaluation — column names are resolved in the data frame
which can silently pick up wrong variables in programmatic use. Use [ with explicit logic in functions.
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Data
PromptBeginner5 minmarkdownQuality: 24
- Matrix indexing a data frame (`df[cbind(i
j)]`) coerces to matrix first — avoid.
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Data
PromptBeginner5 minmarkdownQuality: 28
- Data frame [ with single column: `df[
1]` returns a vector (drop=TRUE default for columns)
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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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