[R] Using lm's subset parameter results in Error in xj[i] : invalid subscript type 'list'

[PIKAL Petr]

Hi

see in line

> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of mviljamaa
> Sent: Tuesday, September 20, 2016 10:01 AM
> To: r-help at r-project.org
> Subject: [R] Using lm's subset parameter results in Error in xj[i] : invalid
> subscript type 'list'
>
> I'm trying to take lm on a subset of my dataset and to do this I believe I need
> to pass my subset of the data as the subset parameter of lm.
>
> So I do my subsetting:
>
> firstkids <- kidmomhsage[0:234,], i.e. the first 234 rows of the data frame.

It works, however line numbering in R starts with 1 not 0. R is clever enough to subset with 0:xx vector however you will not get line 1 by subsetting with 0

dd<-data.frame(a=1:10, b=rnorm(10))
dd[0,]
[1] a b
<0 rows> (or 0-length row.names)

>
> Then construct the model:
>
> fit4 <- lm(kidmomhsage$kid_score ~ kidmomhsage$mom_age +
> kidmomhsage$mom_hs + kidmomhsage$mom_age *
> kidmomhsage$mom_hs,
> subset=firstkids)

You definitelly should spend some time with introductory documentation. The above construction shall be e.g.

fit4 <- lm(kid_score ~ mom_age +mom_hs + mom_age *mom_hs, data = kidmomhsage,  subset=1:234)

>
> which results in:
>
> Error in xj[i] : invalid subscript type 'list'
>
> I read somewhere a recommendation to use "unlist":

I wonder where did you read such recommendation for lm function, you should better avoid that source.

Cheers
Petr

>
> fit4 <- lm(kidmomhsage$kid_score ~ kidmomhsage$mom_age +
> kidmomhsage$mom_hs + kidmomhsage$mom_age *
> kidmomhsage$mom_hs,
> subset=unlist(firstkids))
>
> which seems to not produce the error and results in some sort of model, but
> is this model the correct one (i.e. for the data set firstkids, just as it originally
> appears)? How does unlist change the data?
>
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