General
PromptBeginner5 minmarkdown
- `predict.glm` with `type = response` gives predictions on the response scale (e.g.
probabilities for logistic); `type = link` (default) gives on the link scale.
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General
PromptBeginner5 minmarkdown
- `lowess` parameter is `f` (span
default 2/3); `loess` parameter is `span` (default 0.75).
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General
PromptBeginner5 minmarkdown
- `lowess` is the older function; returns `list(x
y)` — cannot predict at new points.
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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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General
PromptBeginner5 minmarkdown
- Direction: `direction = both` (default)
`forward`
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General
PromptBeginner5 minmarkdown
- For Type III SS
use `car::Anova()` or set contrasts to `contr.sum`/`contr.helmert`.
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General
PromptBeginner5 minmarkdown
- Quasi-families (`quasibinomial`
`quasipoisson`) allow overdispersion — no AIC is computed.
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General
PromptBeginner5 minmarkdown
- `binomial` accepts response as: 0/1 vector
logical
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General
PromptBeginner5 minmarkdown
- `weights` in `glm` means **prior weights** (not frequency weights) — for frequency weights
use the cbind trick or offset.
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General
PromptBeginner5 minmarkdown
- `anova(glm_obj
test = Chisq)` for deviance-based tests; `F` is invalid for non-Gaussian families.
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General
PromptBeginner5 minmarkdown
- Common families: `binomial(link = logit)`
`poisson(link = log)`
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General
PromptBeginner5 minmarkdown
- Default `family = gaussian(link = identity)` — `glm()` with no `family` silently fits OLS (same as `lm`
but slower and with deviance-based output).
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General
PromptBeginner5 minmarkdown
- Column names from `model.matrix` can be surprising: e.g.
`factorLevelName` concatenation.
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General
PromptBeginner5 minmarkdown
- `terms` object attributes: `order` (interaction order per term)
`intercept`
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General
PromptBeginner5 minmarkdown
- `I()` is required to use arithmetic operators literally: `y ~ x + I(x^2)`. Without `I()`
`^` means interaction crossing.
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Coding & Debugging
PromptBeginner5 minmarkdown
- `URLencode(url
reserved = FALSE)` by default does NOT encode reserved chars (`/`
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General
PromptBeginner5 minmarkdown
- Captures output from `cat`
`print`
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General
PromptBeginner5 minmarkdown
> Non-obvious behaviors
gotchas
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General
PromptBeginner5 minmarkdown
- `as.is = TRUE` (recommended): keeps characters as character
not factor.
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General
PromptBeginner5 minmarkdown
- Converts character vectors to appropriate types (logical
integer
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General
PromptBeginner5 minmarkdown
- `formatC(x
format = f
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General
PromptBeginner5 minmarkdown
- `format(x
digits
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General
PromptBeginner5 minmarkdown
- `which = both` (default)
`left`
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General
PromptBeginner5 minmarkdown
- Assignment form: `substr(x
1
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