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- Returns data frame with `size`

`isdir`

- `options(OutDec =

)`: change decimal separator in output (affects `format`

- `file.path(a

- `options(contrasts = c(contr.treatment

contr.poly))`: default contrasts for unordered/ordered factors.

- `options(digits.secs = n)`: max decimal digits for seconds in time formatting (0-6

default 0).

- `options(warn = n)`: -1 = ignore warnings

0 = collect (default)

- `options(digits = n)`: significant digits for printing (1-22

default 7). Suggestion only.

- `options(scipen = n)`: positive biases toward fixed notation

negative toward scientific. Default 0. Applies to `print`/`format`/`cat` but not `sprintf`.

- `system.time(expr)` returns `user`

`system`

- `as.numeric(diff

units = hours)` to extract numeric value in specific units.

- `difftime(time1

time2

- `difftime` arithmetic: subtracting POSIXct objects gives difftime. Units auto-selected (secs

mins

- Explicit units: `secs`

`mins`

- `POSIXlt`: list with components `$sec`

`$min`

- `POSIXct`: seconds since 1970-01-01 UTC (compact

a numeric vector).

- `format(date

%Y)` for year

- `seq.Date(from

- For character sorting

depends on locale. Use `method = radix` for locale-independent fast sorting.

> Non-obvious behaviors

gotchas

- Works on multiple arguments (e.g.

`complete.cases(x

- Default is ascending; use `-x` for descending numeric

or `decreasing = TRUE`.

- Returns a permutation vector of indices

not the sorted values. Use `x[order(x)]` to sort.

- Returns columns named after the grouping variables

with result column keeping the original name.

Data

- If FUN returns multiple values

result column is a **matrix column** inside the data frame.