General
PromptBeginner5 minmarkdown
> Non-obvious behaviors
gotchas
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Showing 24 of 115,675Categories: General, Data, Research & Learning, Cursor-rules, Coding & Debugging
General
PromptBeginner5 minmarkdown
- `I()` is required to use arithmetic operators literally: `y ~ x + I(x^2)`. Without `I()`
`^` means interaction crossing.
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General
PromptBeginner5 minmarkdown
- Captures output from `cat`
`print`
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General
PromptBeginner5 minmarkdown
- `as.is = TRUE` (recommended): keeps characters as character
not factor.
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Coding & Debugging
PromptBeginner5 minmarkdown
- `URLencode(url
reserved = FALSE)` by default does NOT encode reserved chars (`/`
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General
PromptBeginner5 minmarkdown
- `format(x
digits
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General
PromptBeginner5 minmarkdown
- `formatC(x
format = f
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General
PromptBeginner5 minmarkdown
- Converts character vectors to appropriate types (logical
integer
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General
PromptBeginner5 minmarkdown
- `which = both` (default)
`left`
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General
PromptBeginner5 minmarkdown
- `substring(x
first
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General
PromptBeginner5 minmarkdown
- Assignment form: `substr(x
1
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General
PromptBeginner5 minmarkdown
- Returns a **list** (one element per input string)
even for a single string.
3
General
PromptBeginner5 minmarkdown
- Common mistake: unnamed arguments silently match `fixed`
`perl`
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General
PromptBeginner5 minmarkdown
- Three regex modes: POSIX extended (default)
`perl = TRUE`
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General
PromptBeginner5 minmarkdown
- **Name arguments explicitly** — unnamed args after `x`/`pattern` are matched positionally to `ignore.case`
`perl`
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General
PromptBeginner5 minmarkdown
- `read.csv` defaults differ from `read.table`: `header = TRUE`
`sep =
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General
PromptBeginner5 minmarkdown
> Non-obvious behaviors
gotchas
2
General
PromptBeginner5 minmarkdown
- `sep = "` (default) means **any whitespace** (spaces
tabs
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General
PromptBeginner5 minmarkdown
- `file_test(-nt
f1
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General
PromptBeginner5 minmarkdown
- `file_test(-f
path)`: TRUE if regular file exists.
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General
PromptBeginner5 minmarkdown
- `file_test(-d
path)`: TRUE if directory exists.
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Data
PromptBeginner5 minmarkdown
- Returns data frame with `size`
`isdir`
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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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