Creative
PromptBeginner5 minmarkdown
- `aov` is a wrapper around `lm` that stores extra info for balanced ANOVA. For unbalanced designs
Type I SS (sequential) are computed — order of terms matters.
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Creative
PromptBeginner5 minmarkdown
- `model.matrix` creates the design matrix including dummy coding. Default contrasts: `contr.treatment` for unordered factors
`contr.poly` for ordered.
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Coding & Debugging
PromptBeginner5 minmarkdown
- `URLencode(url
reserved = FALSE)` by default does NOT encode reserved chars (`/`
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Creative
PromptBeginner5 minmarkdown
- `substr(x
start
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Data
PromptBeginner5 minmarkdown
- Returns data frame with `size`
`isdir`
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Data
PromptBeginner5 minmarkdown
- If FUN returns multiple values
result column is a **matrix column** inside the data frame.
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Data
PromptBeginner5 minmarkdown
- Formula interface (`aggregate(y ~ x
data
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Coding & Debugging
PromptBeginner5 minmarkdown
- `as.numeric(f)` returns **integer codes**
not original values. Use `as.numeric(levels(f))[f]` or `as.numeric(as.character(f))`.
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Data
PromptBeginner5 minmarkdown
- For data frames
operates on whole rows. For lists
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Data
PromptBeginner5 minmarkdown
- `rbind` on data frames matches columns **by name**
not position. Missing columns get `NA`.
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Data
PromptBeginner5 minmarkdown
- Result is always an **array** (even 1D)
class table. Convert to data frame with `as.data.frame(tbl)`.
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Data
PromptBeginner5 minmarkdown
- `cbind` on data frames calls `data.frame(...)`
not `cbind.matrix`. Mixing matrices and data frames can give unexpected results.
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Data
PromptBeginner5 minmarkdown
- Default `by` is `intersect(names(x)
names(y))` — can silently merge on unintended columns if data frames share column names.
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Data
PromptBeginner5 minmarkdown
- Returns an **array** (not a data frame). Class info on return values is **discarded** (e.g.
Date objects become numeric).
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Data
PromptBeginner5 minmarkdown
- On a **data frame**
`apply` coerces to matrix via `as.matrix` first — mixed types become character.
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Data
PromptBeginner5 minmarkdown
- Matrix indexing a data frame (`df[cbind(i
j)]`) coerces to matrix first — avoid.
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Data
PromptBeginner5 minmarkdown
- Data frame `[` with single column: `df[
1]` returns a **vector** (drop=TRUE default for columns)
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Data
PromptBeginner5 minmarkdown
- `subset` argument uses **non-standard evaluation** — column names are resolved in the data frame
which can silently pick up wrong variables in programmatic use. Use `[` with explicit logic in functions.
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Coding & Debugging
PromptBeginner5 minmarkdown
- Factor indexing: `x[f]` uses integer codes of factor `f`
not its character labels. Use `x[as.character(f)]` for label-based indexing.
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Data
PromptBeginner5 minmarkdown
- `ts(data
start
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Data
PromptBeginner5 minmarkdown
- `relist(flesh
skeleton)` — `flesh` is the flat data
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Creative
PromptBeginner5 minmarkdown
- `tryCatch(expr
warning = function(w) {...})` catches the **first** warning and exits. Use `withCallingHandlers` + `invokeRestart(muffleWarning)` to suppress warnings but continue.
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Creative
PromptBeginner5 minmarkdown
- `Reduce` with `init` adds a starting value: `Reduce(f
x
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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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