CODEWITHSUNDEEP
rregressionlinear-regression
Doug Fir
Doug Fir

Reputation: 21292

Cannot use poly(x) within a loop? 'degree' must be less than number of unique points

library(ISLR)

Choosing a model based on any feature:

amodel <- lm(crim ~ poly(dat$zn, 3), data = Boston)

Works, returns a model. When I try to do this with every variable in a loop I get:

dat <- dplyr::select(Boston, -crim)
sapply(dat, function(x) {
  mod <- lm(crim ~ poly(x, 3), data = Boston)
  summary(mod)
})

Error in poly(x, 3) : 'degree' must be less than number of unique points

How can I get this to run within a loop? I would like to create a model for each poly(feature, 3) in Boston (minus crim feature).

Upvotes: 0

Views: 1451

Answers (1)

dynamicwebpaige
dynamicwebpaige

Reputation: 393

Numerical overflow would be my guess. If you dig into the code for poly, you'll see that it generates the individual polynomial terms as an intermediate step:

X <- outer(x, seq_len(n) - 1, "^")

and when n (the degree of the polynomial you want) is 3, combined with the code used to generate the linear model lm(), the resulting terms go up to exponentially.

Upvotes: 1

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