General
PromptBeginner5 minmarkdown
- `system.time(expr)` returns `user`
`system`
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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
- `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
- Explicit units: `secs`
`mins`
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General
PromptBeginner5 minmarkdown
- `POSIXlt`: list with components `$sec`
`$min`
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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
- `seq.Date(from
to
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General
PromptBeginner5 minmarkdown
> Non-obvious behaviors
gotchas
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General
PromptBeginner5 minmarkdown
- `format(date
%Y)` for year
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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
- Default is ascending; use `-x` for descending numeric
or `decreasing = TRUE`.
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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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Data
PromptBeginner5 minmarkdown
- If FUN returns multiple values
result column is a **matrix column** inside the data frame.
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General
PromptBeginner5 minmarkdown
- Works on multiple arguments (e.g.
`complete.cases(x
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General
PromptBeginner5 minmarkdown
- Returns columns named after the grouping variables
with result column keeping the original name.
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General
PromptBeginner5 minmarkdown
- Levels are sorted by default
but sort order is **locale-dependent** at creation time.
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General
PromptBeginner5 minmarkdown
- `c()` on factors unions level sets (since R 4.1.0)
but earlier versions converted to integer.
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Data
PromptBeginner5 minmarkdown
- Formula interface (`aggregate(y ~ x
data
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General
PromptBeginner5 minmarkdown
- Only `==` and `!=` work between factors; factors must have identical level sets. Ordered factors support `<`
`>`.
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General
PromptBeginner5 minmarkdown
- Duplicate column names allowed only with `check.names = FALSE`
but many operations will de-dup them silently.
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Coding & Debugging
PromptBeginner5 minmarkdown
- `as.numeric(f)` returns **integer codes**
not original values. Use `as.numeric(levels(f))[f]` or `as.numeric(as.character(f))`.
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General
PromptBeginner5 minmarkdown
- `duplicated` marks the **second and later** occurrences as TRUE
not the first. Use `fromLast = TRUE` to reverse.
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