Creative
PromptBeginner5 minmarkdownQuality: 26
- model.matrix creates the design matrix including dummy coding. Default contrasts: contr.treatment...
contr.poly for ordered.
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Creative
PromptBeginner5 minmarkdownQuality: 22
- `substr(x
start
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Data
PromptBeginner5 minmarkdownQuality: 22
- Returns data frame with size
isdir
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Data
PromptBeginner5 minmarkdownQuality: 22
- If FUN returns multiple values
result column is a matrix column inside the data frame.
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Data
PromptBeginner5 minmarkdownQuality: 22
- Formula interface (`aggregate(y ~ x
data
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Data
PromptBeginner5 minmarkdownQuality: 22
- For data frames
operates on whole rows. For lists
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Data
PromptBeginner5 minmarkdownQuality: 22
- rbind on data frames matches columns by name
not position. Missing columns get NA.
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Data
PromptBeginner5 minmarkdownQuality: 26
- 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: 26
- cbind on data frames calls data.frame(...)
not cbind.matrix. Mixing matrices and data frames can give unexpected results.
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Data
PromptBeginner5 minmarkdownQuality: 26
- 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: 26
- Returns an array (not a data frame). Class info on return values is discarded (e.g.
Date objects become numeric).
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Data
PromptBeginner5 minmarkdownQuality: 26
- On a data frame
apply coerces to matrix via as.matrix first — mixed types become character.
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Data
PromptBeginner5 minmarkdownQuality: 22
- Matrix indexing a data frame (`df[cbind(i
j)]`) coerces to matrix first — avoid.
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Data
PromptBeginner5 minmarkdownQuality: 26
- Data frame [ with single column: `df[
1]` returns a vector (drop=TRUE default for columns)
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Data
PromptBeginner5 minmarkdownQuality: 26
- 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: 22
- `ts(data
start
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Data
PromptBeginner5 minmarkdownQuality: 22
- `relist(flesh
skeleton) — flesh` is the flat data
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Creative
PromptBeginner5 minmarkdownQuality: 26
- `tryCatch(expr
warning = function(w) {...}) catches the first warning and exits. Use withCallingHandlers + invokeRestart(muffleWarning)` to suppress warnings but continue.
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Creative
PromptBeginner5 minmarkdownQuality: 22
- Reduce with init adds a starting value: `Reduce(f
x
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Data
PromptBeginner5 minmarkdownQuality: 22
- Useful pattern: `do.call(rbind
listofdfs)` to combine a list of data frames.
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Data
PromptBeginner5 minmarkdownQuality: 26
- io-and-text.md — Read when: read.table silently drops data or misparses columns
regex behaves differently than expected
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Data
PromptBeginner5 minmarkdownQuality: 26
- visualization.md — Read when: par settings reset unexpectedly
layout/mfrow interaction is confusing
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Data
PromptBeginner5 minmarkdownQuality: 26
- statistics.md — Read when: hypothesis test gives surprising result
need to choose correct p.adjust method
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Data
PromptBeginner5 minmarkdownQuality: 26
- data-wrangling.md — Read when: subsetting returns wrong type
apply on data frame gives unexpected coercion
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