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
- Quasi-families (`quasibinomial`
`quasipoisson`) allow overdispersion — no AIC is computed.
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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
- `binomial` accepts response as: 0/1 vector
logical
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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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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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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
> Non-obvious behaviors
gotchas
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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
- `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
- `which = both` (default)
`left`
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General
PromptBeginner5 minmarkdown
- `format(x
digits
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Creative
PromptBeginner5 minmarkdown
- `substr(x
start
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General
PromptBeginner5 minmarkdown
- Assignment form: `substr(x
1
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General
PromptBeginner5 minmarkdown
- `substring(x
first
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General
PromptBeginner5 minmarkdown
- Common mistake: unnamed arguments silently match `fixed`
`perl`
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General
PromptBeginner5 minmarkdown
- **Name arguments explicitly** — unnamed args after `x`/`pattern` are matched positionally to `ignore.case`
`perl`
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General
PromptBeginner5 minmarkdown
- Returns a **list** (one element per input string)
even for a single string.
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