How do I pass a string to an object inside an R function?

Question

I have a more complicated function that I am working on. I want to pass a variable around inside of my function to do several things. The part that is not working is trying to access an object that has my variable's name embedded in it.

A simple example would be as follows:

    ## Annette Dobson (1990) "An Introduction to Generalized Linear Models".
    ## Page 9: Plant Weight Data.

    ctl <- c(4.17,5.58,5.18,6.11,4.50,4.61,5.17,4.53,5.33,5.14)
    trt <- c(4.81,4.17,4.41,3.59,5.87,3.83,6.03,4.89,4.32,4.69)
    group <- gl(2,10,20, labels=c("Ctl","Trt"))
    weight <- c(ctl, trt)

    D9.fit.lm <- lm(weight ~ group)

    my.coeff <- function(mname)
       {
        b  <-  round(mname.fit.lm$coef[1],2)
        m  <-  round(mname.fit.lm$coef[2],4)
        r2 <-  round(summary(mname.fit.lm)$r.squared,2)

        cbind(b, m, r2)
       }

So if I try this bit of code like this:

 my.coeff("D9")

Then I get the following error:

 Error in my.coeff("D9") : object 'mname.fit.lm' not found

I really my function to work and it should look like this output

 cbind(round(D9.fit.lm$coef[1],2),round(D9.fit.lm$coef[2],4),round(summary(D9.fit.lm)$r.squared,2))
             [,1]   [,2] [,3]
 (Intercept) 5.03 -0.371 0.07

Thanks !

Ramnath · Accepted Answer · 2011-11-18 22:04:33Z

4

Just add this line inside you function

mname.fit.lm <- get(paste(mname, ".fit.lm", sep = ""))

edited Nov 18, 2011 at 22:04

answered Nov 18, 2011 at 21:55

Ramnath

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1 Comment

user918967 Over a year ago

Aside from missing a parenthesis this does it ! mname.fit.lm <- get(paste(mname, ".fit.lm", sep = "")) Thanks !!

JD Long · Accepted Answer · 2011-11-18 21:54:30Z

1

you're passing a character string into your function. It looks like you should possibly be passing a lm object.

so something like this:

my.coeff <- function(mname)
{
  b  <-  round(mname$coef[1],2)
  m  <-  round(mname$coef[2],4)
  r2 <-  round(summary(mname)$r.squared,2)

  cbind(b, m, r2)
}

my.coeff(D9.fit.lm)

answered Nov 18, 2011 at 21:54

JD Long

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1 Comment

Carl Witthoft Over a year ago

I believe this is the approach recommended in the R Inferno.

joran · Accepted Answer · 2011-11-18 21:59:16Z

1

As Ramnath says, sometimes people solve this problem with get. But I agree with JD that in this case you should just choose a better way of storing your lm objects. Another option is to store them in a named list:

fit.lm <- list()
fit.lm[["D9"]] <- lm(weight ~ group)

my.coeff <- function(mname)
{
    b  <-  round(fit.lm[[mname]]$coef[1],2)
    m  <-  round(fit.lm[[mname]]$coef[2],4)
    r2 <-  round(summary(fit.lm[[mname]])$r.squared,2)

    cbind(b, m, r2)
}

answered Nov 18, 2011 at 21:59

joran

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