[R] Problems with subset, droplevels and lm: variable lengths differ

[Peter Ehlers]

On 2012-04-16 10:43, Michael Friendly wrote:
> [Env:  R 2.14.2 / Win Xp]
>
> In the script below, I want to select some variables from
> rrcov::OsloTransect, delete cases with
> any missing data, and subset the data frame Oslo to remove cases for two
> levels of the
> factor litho that occur with low frequency.
>
> The checks I run on my new data frame Oslo look OK, but I when I try to
> fit a multivariate
> linear model with lm(), I am getting an error: variable lengths differ
> (found for 'litho').
> How can I fix this?
>
>   >  data(OsloTransect, package="rrcov")
>   >  # keep a subset of variables&  rename some variables
>   >  Oslo<-OsloTransect[c("X.ID", "XCOO", "YCOO", "X.FOREST",
> "X.WEATHER", "X.FLITHO", "ALT")]
>   >  colnames(Oslo)<- c("site", "XC", "YC", "forest", "weather", "litho",
> "altitude")
>   >  Oslo<- cbind(Oslo, OsloTransect[,c("Cu", "Fe", "K", "Mg", "Mn", "P",
> "Zn")])
>   >  # make site a factor
>   >  Oslo[,"site"]<- factor(Oslo[,"site"])
>   >
>   >  # log transform the chemical elements
>   >  Oslo[,8:14]<- log(Oslo[,8:14])
>   >
>   >  # delete cases with missing data
>   >  Oslo<- Oslo[complete.cases(Oslo),]
>   >  nrow(Oslo)
> [1] 350
>   >
>   >  # delete low frequency litho=="GNEID_O" | "MICSH"
>   >  Oslo<- subset(Oslo, !litho %in% c("GNEID_O", "MICSH"), drop=TRUE)
>   >  nrow(Oslo)
> [1] 332
>   >  Oslo<- droplevels(Oslo)
>   >  table(Oslo$litho)
>
>    CAMSED GNEIS_O GNEIS_R    MAGM
>        98      89      32     113
>   >  nrow(Oslo)
> [1] 332
>   >  mod1<- lm(cbind("Cu", "Fe", "K", "Mg", "Mn", "P", "Zn") ~ litho +
> forest + weather, data=Oslo)
> Error in model.frame.default(formula = cbind("Cu", "Fe", "K", "Mg",
> "Mn",  :
>     variable lengths differ (found for 'litho')
>   >
>

Michael,
Unless I'm missing something, don't you just have to drop the quotes
in your cbind()?

Peter Ehlers