General
PromptBeginner5 minmarkdownQuality: 24
- Tests near equality with tolerance (default 1.5e-8
i.e.
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General
PromptBeginner5 minmarkdownQuality: 28
- Returns TRUE or a character string describing the difference — NOT FALSE. Use `isTRUE(all.equal(x
y))` in conditionals.
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General
PromptBeginner5 minmarkdownQuality: 24
- Custom conditions: `stop(errorCondition(msg
class = myError)) then catch with tryCatch(...
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General
PromptBeginner5 minmarkdownQuality: 28
- tryCatch unwinds the call stack — handler runs in the calling environment
not where the error occurred. Cannot resume execution.
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Creative
PromptBeginner5 minmarkdownQuality: 28
- `tryCatch(expr
warning = function(w) {...}) catches the first warning and exits. Use withCallingHandlers + invokeRestart(muffleWarning)` to suppress warnings but continue.
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General
PromptBeginner5 minmarkdownQuality: 24
- `tryCatch(expr
error = function(e) e)` returns the error condition object.
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General
PromptBeginner5 minmarkdownQuality: 24
- `Position(f
x) returns the index of the first match (like Find` but returns position
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General
PromptBeginner5 minmarkdownQuality: 28
- lengths(x) returns the length of each element of a list. Equivalent to `sapply(x
length)` but faster (implemented in C).
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General
PromptBeginner5 minmarkdownQuality: 24
- `Find(f
x) returns the first element where f(elem) is TRUE. Find(f
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General
PromptBeginner5 minmarkdownQuality: 24
- `Map(f
...) is a simple wrapper for mapply(f
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Creative
PromptBeginner5 minmarkdownQuality: 24
- Reduce with init adds a starting value: `Reduce(f
x
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General
PromptBeginner5 minmarkdownQuality: 24
- `Filter(f
x) keeps elements where f(elem) is TRUE. Unlike x[sapply(x
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General
PromptBeginner5 minmarkdownQuality: 24
- `Reduce(f
x
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General
PromptBeginner5 minmarkdownQuality: 24
- `Reduce(f
x
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General
PromptBeginner5 minmarkdownQuality: 24
- `Reduce(f
x) applies binary function f cumulatively: Reduce(+
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General
PromptBeginner5 minmarkdownQuality: 24
- `do.call(fun
args_list) — args` must be a list
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Data
PromptBeginner5 minmarkdownQuality: 24
- Useful pattern: `do.call(rbind
listofdfs)` to combine a list of data frames.
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General
PromptBeginner5 minmarkdownQuality: 24
Non-obvious behaviors
gotchas
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General
PromptBeginner5 minmarkdownQuality: 24
- Use stop()
warning()
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General
PromptBeginner5 minmarkdownQuality: 24
- `with(df
expr) avoids repeating df$` everywhere
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General
PromptBeginner5 minmarkdownQuality: 28
- misc-utilities.md — Read when: do.call behaves differently than direct call
need Reduce/Filter/Map
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General
PromptBeginner5 minmarkdownQuality: 28
- dates-and-system.md — Read when: Date/POSIXct conversion gives wrong day
time zones cause off-by-one
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Data
PromptBeginner5 minmarkdownQuality: 28
- io-and-text.md — Read when: read.table silently drops data or misparses columns
regex behaves differently than expected
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Data
PromptBeginner5 minmarkdownQuality: 28
- visualization.md — Read when: par settings reset unexpectedly
layout/mfrow interaction is confusing
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