Find agent skills by outcome

- `Reduce` with `init` adds a starting value: `Reduce(f

- `Filter(f

x)` keeps elements where `f(elem)` is `TRUE`. Unlike `x[sapply(x

- `Reduce(f

- `Reduce(f

- `Reduce(f

x)` applies binary function `f` cumulatively: `Reduce(+

- Useful pattern: `do.call(rbind

list_of_dfs)` to combine a list of data frames.

- `do.call(fun

args_list)` — `args` must be a **list**

> Non-obvious behaviors

gotchas

- `with(df

expr)` avoids repeating `df$` everywhere

- Use `stop()`

`warning()`

- misc-utilities.md — Read when: do.call behaves differently than direct call

need Reduce/Filter/Map

- dates-and-system.md — Read when: Date/POSIXct conversion gives wrong day

time zones cause off-by-one

- io-and-text.md — Read when: read.table silently drops data or misparses columns

regex behaves differently than expected

- visualization.md — Read when: par settings reset unexpectedly

layout/mfrow interaction is confusing

- statistics.md — Read when: hypothesis test gives surprising result

need to choose correct p.adjust method

- modeling.md — Read when: formula syntax is confusing (`I()`

`*` vs `:`

- data-wrangling.md — Read when: subsetting returns wrong type

apply on data frame gives unexpected coercion

For deeper coverage

read the reference files in `references/`:

Non-obvious behaviors

surprising defaults

labels = c(low

med

df$category <- cut(df$value

breaks = c(0

rbind(df1

df2) # stack rows (same columns)

cbind(df1

df2) # bind columns (same rows)

df[!duplicated(df$id)

]