General
PromptBeginner5 minmarkdown
- **Does** add new names not in `x` — it uses `x[names(val)] <- val` internally
so any name in `val` gets added or replaced.
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Showing 24 of 109,525Categories: Writing & Content, General, Cursor-rules, Coding & Debugging
General
PromptBeginner5 minmarkdown
- `modifyList(x
val)` replaces elements of list `x` with those in `val` by **name**.
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General
PromptBeginner5 minmarkdown
- `FUN` argument applies a function to each combination: `combn(5
3
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General
PromptBeginner5 minmarkdown
- Checks attributes
names
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General
PromptBeginner5 minmarkdown
- `combn(n
m)` or `combn(x
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General
PromptBeginner5 minmarkdown
- 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 minmarkdown
- Custom conditions: `stop(errorCondition(msg
class = myError))` then catch with `tryCatch(...
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General
PromptBeginner5 minmarkdown
- Tests **near equality** with tolerance (default `1.5e-8`
i.e.
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General
PromptBeginner5 minmarkdown
- `tryCatch(expr
error = function(e) e)` returns the error condition object.
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General
PromptBeginner5 minmarkdown
- `tryCatch` **unwinds** the call stack — handler runs in the calling environment
not where the error occurred. Cannot resume execution.
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General
PromptBeginner5 minmarkdown
- `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 minmarkdown
- `Find(f
x)` returns the **first** element where `f(elem)` is `TRUE`. `Find(f
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General
PromptBeginner5 minmarkdown
- `Position(f
x)` returns the **index** of the first match (like `Find` but returns position
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General
PromptBeginner5 minmarkdown
- `Map(f
...)` is a simple wrapper for `mapply(f
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General
PromptBeginner5 minmarkdown
- `Filter(f
x)` keeps elements where `f(elem)` is `TRUE`. Unlike `x[sapply(x
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General
PromptBeginner5 minmarkdown
- `Reduce(f
x
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General
PromptBeginner5 minmarkdown
- `Reduce(f
x
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General
PromptBeginner5 minmarkdown
- `Reduce(f
x)` applies binary function `f` cumulatively: `Reduce(+
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General
PromptBeginner5 minmarkdown
- `do.call(fun
args_list)` — `args` must be a **list**
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General
PromptBeginner5 minmarkdown
> Non-obvious behaviors
gotchas
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General
PromptBeginner5 minmarkdown
- `with(df
expr)` avoids repeating `df$` everywhere
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General
PromptBeginner5 minmarkdown
- Use `stop()`
`warning()`
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General
PromptBeginner5 minmarkdown
- **misc-utilities.md** — Read when: do.call behaves differently than direct call
need Reduce/Filter/Map
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General
PromptBeginner5 minmarkdown
- **dates-and-system.md** — Read when: Date/POSIXct conversion gives wrong day
time zones cause off-by-one
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