Data
PromptBeginner5 minmarkdown
- Formula interface: `cor.test(~ x + y
data = df)` — note the `~` with no LHS.
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Data
PromptBeginner5 minmarkdown
- Default kernel: `gaussian`. Range of density extends beyond data range (controlled by `cut`
default 3 bandwidths).
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Data
PromptBeginner5 minmarkdown
- Default bandwidth: `bw = nrd0` (Silverman's rule of thumb). For multimodal data
consider `SJ` or `bcv`.
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Creative
PromptBeginner5 minmarkdown
- `nstart > 1` recommended (e.g.
`nstart = 25`): runs algorithm from multiple random starts
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Data
PromptBeginner5 minmarkdown
- For composite hypotheses (parameters estimated from data)
p-values are **conservative** (too large). Use `dgof` or `ks.test` with `exact = NULL` for discrete distributions.
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Data
PromptBeginner5 minmarkdown
- Returns a matrix of p-values
not test statistics.
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Coding & Debugging
PromptBeginner5 minmarkdown
- `SANN` (simulated annealing): convergence code is **always 0** — it never fails. `maxit` = total function evals (default 10000)
no other stopping criterion.
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Data
PromptBeginner5 minmarkdown
- If data fits too exactly (no residual noise)
convergence check fails — use `control = list(scaleOffset = 1)` or jitter data.
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Creative
PromptBeginner5 minmarkdown
- Self-starting models (`SSlogis`
`SSasymp`
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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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Writing & Content
PromptBeginner5 minmarkdown
- `write.csv` fixes `sep =
`
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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
- 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
- `rbind` on data frames matches columns **by name**
not position. Missing columns get `NA`.
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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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