General
PromptBeginner5 minmarkdown
> Non-obvious behaviors
gotchas
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General
PromptBeginner5 minmarkdown
- `file_test(-f
path)`: TRUE if regular file exists.
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General
PromptBeginner5 minmarkdown
- On some filesystems
`ctime` is status-change time
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General
PromptBeginner5 minmarkdown
- `list.files(pattern = *.csv)` — `pattern` is a **regex**
not a glob! Use `glob2rx(*.csv)` or `\\.csv$`.
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General
PromptBeginner5 minmarkdown
- `file.path(a
b
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General
PromptBeginner5 minmarkdown
- `options(contrasts = c(contr.treatment
contr.poly))`: default contrasts for unordered/ordered factors.
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General
PromptBeginner5 minmarkdown
- `options(warn = n)`: -1 = ignore warnings
0 = collect (default)
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General
PromptBeginner5 minmarkdown
- `options(OutDec =
)`: change decimal separator in output (affects `format`
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General
PromptBeginner5 minmarkdown
- `options(digits.secs = n)`: max decimal digits for seconds in time formatting (0-6
default 0).
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General
PromptBeginner5 minmarkdown
- `options(digits = n)`: significant digits for printing (1-22
default 7). Suggestion only.
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General
PromptBeginner5 minmarkdown
- `options(scipen = n)`: positive biases toward fixed notation
negative toward scientific. Default 0. Applies to `print`/`format`/`cat` but not `sprintf`.
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General
PromptBeginner5 minmarkdown
- `system.time(expr)` returns `user`
`system`
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General
PromptBeginner5 minmarkdown
- Explicit units: `secs`
`mins`
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General
PromptBeginner5 minmarkdown
- `as.numeric(diff
units = hours)` to extract numeric value in specific units.
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General
PromptBeginner5 minmarkdown
- `difftime(time1
time2
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General
PromptBeginner5 minmarkdown
- `difftime` arithmetic: subtracting POSIXct objects gives difftime. Units auto-selected (secs
mins
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General
PromptBeginner5 minmarkdown
- `POSIXct`: seconds since 1970-01-01 UTC (compact
a numeric vector).
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General
PromptBeginner5 minmarkdown
- `POSIXlt`: list with components `$sec`
`$min`
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General
PromptBeginner5 minmarkdown
- `seq.Date(from
to
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General
PromptBeginner5 minmarkdown
- `format(date
%Y)` for year
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General
PromptBeginner5 minmarkdown
> Non-obvious behaviors
gotchas
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General
PromptBeginner5 minmarkdown
- Default is ascending; use `-x` for descending numeric
or `decreasing = TRUE`.
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General
PromptBeginner5 minmarkdown
- For character sorting
depends on locale. Use `method = radix` for locale-independent fast sorting.
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General
PromptBeginner5 minmarkdown
- Returns a **permutation vector** of indices
not the sorted values. Use `x[order(x)]` to sort.
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