Data
PromptBeginner5 minmarkdown
- `rbind` on data frames matches columns **by name**
not position. Missing columns get `NA`.
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General
PromptBeginner5 minmarkdown
- Supports formula syntax: `split(df
~ Month)`.
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General
PromptBeginner5 minmarkdown
- 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 minmarkdown
- `by = 0` or `by = row.names` merges on row names
adding a Row.names column.
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General
PromptBeginner5 minmarkdown
- `...` 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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Data
PromptBeginner5 minmarkdown
- 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 minmarkdown
- 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 minmarkdown
- `...` args cannot share names with `X`
`MARGIN`
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General
PromptBeginner5 minmarkdown
- Return value orientation is transposed: if FUN returns length-n vector
result has dim `c(n
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General
PromptBeginner5 minmarkdown
- `sapply` can return a vector
matrix
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General
PromptBeginner5 minmarkdown
- Factors
raw vectors
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Data
PromptBeginner5 minmarkdown
- `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 minmarkdown
- On a **data frame**
`apply` coerces to matrix via `as.matrix` first — mixed types become character.
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Data
PromptBeginner5 minmarkdown
- Data frame `[` with single column: `df[
1]` returns a **vector** (drop=TRUE default for columns)
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Data
PromptBeginner5 minmarkdown
- Matrix indexing a data frame (`df[cbind(i
j)]`) coerces to matrix first — avoid.
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Coding & Debugging
PromptBeginner5 minmarkdown
- 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 minmarkdown
> Non-obvious behaviors
gotchas
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General
PromptBeginner5 minmarkdown
- `m[j = 2
i = 1]` is `m[2
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General
PromptBeginner5 minmarkdown
- `stl` result components: `$time.series` matrix with columns `seasonal`
`trend`
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General
PromptBeginner5 minmarkdown
- `stl` requires `s.window` (seasonal window) — must be specified
no default. `s.window = periodic` assumes fixed seasonality.
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General
PromptBeginner5 minmarkdown
- `decompose`: simpler than `stl`
uses moving averages. `type = additive` or `multiplicative`.
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General
PromptBeginner5 minmarkdown
- `arima(x
order = c(p
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General
PromptBeginner5 minmarkdown
- `format(object.size(x)
units = MB)` for human-readable output.
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Data
PromptBeginner5 minmarkdown
- `ts(data
start
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