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
- `Filter(f
x)` keeps elements where `f(elem)` is `TRUE`. Unlike `x[sapply(x
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General
PromptBeginner5 minmarkdown
- `Map(f
...)` is a simple wrapper for `mapply(f
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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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Data
PromptBeginner5 minmarkdown
- Useful pattern: `do.call(rbind
list_of_dfs)` to combine a list of data frames.
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General
PromptBeginner5 minmarkdown
- `with(df
expr)` avoids repeating `df$` everywhere
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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
- Use `stop()`
`warning()`
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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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Data
PromptBeginner5 minmarkdown
- **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 minmarkdown
- **visualization.md** — Read when: par settings reset unexpectedly
layout/mfrow interaction is confusing
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Data
PromptBeginner5 minmarkdown
- **statistics.md** — Read when: hypothesis test gives surprising result
need to choose correct p.adjust method
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General
PromptBeginner5 minmarkdown
- **modeling.md** — Read when: formula syntax is confusing (`I()`
`*` vs `:`
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Data
PromptBeginner5 minmarkdown
- **data-wrangling.md** — Read when: subsetting returns wrong type
apply on data frame gives unexpected coercion
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General
PromptBeginner5 minmarkdown
For deeper coverage
read the reference files in `references/`:
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General
PromptBeginner5 minmarkdown
Non-obvious behaviors
surprising defaults
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General
PromptBeginner5 minmarkdown
labels = c(low
med
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General
PromptBeginner5 minmarkdown
rbind(df1
df2) # stack rows (same columns)
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General
PromptBeginner5 minmarkdown
cbind(df1
df2) # bind columns (same rows)
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General
PromptBeginner5 minmarkdown
df$category <- cut(df$value
breaks = c(0
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