Storing model (e.g., lm) in list changes its class

Question

I am storing lm models in a list and then want to use loops to access a specific model to extract results. Specifically, I have code like this:

model1 <- lm(dv ~ group,data=df,na.action=na.omit)
model2 <- lm(dv ~ cov + group,data=df,na.action=na.omit)
model3 <- lm(dv ~ group,data=df_out,na.action=na.omit)
model4 <- lm(dv ~ cov + group,data=df_out,na.action=na.omit)

lom <- list(main=model1,main_cov=model2,main_out=model3, main_cov_out=model4)

for (x in c(1:length(lom))) {
    for (y in c(1:length(lom[[x]]))) {
        modl <- lolom[[x]][y]
        class(modl) <- "lm" 
        anov <- Anova(modl,type="II") # (from Car package)
        } # (y in c(1:length(lom[[x]])))
    } # (x in c(1:length(lom)))

but get this error...

Error in terms.default(object) : no terms component nor attribute In addition: Warning message: In is.na(coef(mod)) : is.na() applied to non-(list or vector) of type 'NULL'

I checked the class of "modl" and it was "list" so I tried to change the class hoping that Anova would then be able to access all the relevant information contained in the lm object, but to no avail. I know the whole object is actually stored in the list by checking names and accessing different levels of the modl object (e.g., modl$model).

aatrujillob · Accepted Answer · 2012-03-28 05:29:38Z

3

Maybe lapply(lom, Anova,type="II") ?

and if you want a list of all the objects:

lapply(lom, function(x) lapply(seq_along(names(x)), function(i) x[i]))

edited Mar 28, 2012 at 5:29

answered Mar 28, 2012 at 5:20

aatrujillob

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2 Comments

dmac Over a year ago

Thank you. Although it's hard for me to follow the double embedded lapply, this response has opened things up for me. Specifically, I finally am getting how lapply should be used instead of loops and the level of dynamic coding possible for me has increased by an order of magnitude.

WillZ Over a year ago

Sorry if I missed anything, but this doesn't really address the question on why the mode of the objects where changed when calling list()?

Matthew Lundberg · Accepted Answer · 2012-03-28 05:19:12Z

1

(Assuming that you really mean lom[[x]][y] and lolom is a typo.)

Too many loops?

You want to run Anova on each model, that is, each entry of the list:

for (x in 1:length(lom)) {
    modl <- lom[[x]]
    # etc
}

answered Mar 28, 2012 at 5:19

Matthew Lundberg

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