[R] store list objects in data.table

[Rui Barradas]

Às 22:25 de 21/09/2024, Naresh Gurbuxani escreveu:
> I am trying to store regression objects in a data.table
> 
> df <- data.frame(x = rnorm(20))
> df[, "y"] <- with(df, x + 0.1 * x^2 + 0.2 * rnorm(20))
> 
> mydt <- data.table(mypower = c(1, 2), myreg = list(lm(y ~ x, data = df),
> lm(y ~ x + I(x^2), data = df)))
> 
> mydt
> #   mypower    myreg
> #     <num>   <list>
> #1:       1 <lm[12]>
> #2:       2 <lm[12]>
> 
> But mydt[1, 2] has only the coeffients of the first regression. mydt[2,
> 2] has residuals of the first regression.  These are the first two
> components of "lm" object.
> 
> mydt[1, myreg[[1]]]
> #(Intercept)           x
> #   0.107245    1.034110
> 
> Is there a way to put full "lm" object in each row?
> 
> Thanks,
> Naresh
> 
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Hello,

Yes, there are ways of pulling the full lm objects from the list column. 
It's a matter of using the right indexing.

mydt[[2L]][1L] extracts a list whose element is a lm object.
mydt[[2L]][[1L]] extracts yhe lm object, this is the one you want.

See the two examples below.



library(data.table)

df <- data.frame(x = rnorm(20))
df[, "y"] <- with(df, x + 0.1 * x^2 + 0.2 * rnorm(20))

mydt <- data.table(
   mypower = c(1, 2),
   myreg = list(lm(y ~ x, data = df),
                lm(y ~ x + I(x^2), data = df)))

mydt[[2L]][1L] |> class()
#> [1] "list"

mydt[[2L]][[1L]] |> class()
#> [1] "lm"


Hope this helps,

Rui Barradas



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