Question

How to change function argument name. For example using substitute I can change function argument value or function name:

substitute(quote(F(x= A)), list(A= quote(B), F= quote(G)))
## result
quote(G(x = B))

but this doesn’t work:

substitute(quote(F(x= A)), list(x= quote(y)))
## result
quote(F(x = A))

#
EDIT (@Joran here is real example, maybe not so real but very close to what I am doing)

#

library("multcomp")
data("mtcars")

mtcars$gear <- factor(mtcars$gear)
mtcars$cyl <- factor(mtcars$cyl)
xv <- c("gear","cyl")

for(v in xv){
 fo <- as.formula(paste("mpg",v,sep="~"))
 fit <- lm(fo,data=mtcars)
 print(eval(substitute(summary(glht(fit,linfct= mcp(vn="Dunnett"))),list(vn=v))))
}

Answer 1

Taking your example of something similar to the actual problem, why not do this:

library("multcomp")
data("mtcars")

mtcars$gear <- factor(mtcars$gear)
mtcars$cyl <- factor(mtcars$cyl)
xv <- c("gear","cyl")

ll <- list("Dunnett")
for(v in xv){
  fo <- as.formula(paste("mpg",v,sep="~"))
  fit <- lm(fo,data=mtcars)
  names(ll) <- v
  print(summary(glht(fit, linfct = do.call(mcp, ll))))
}

Which gives:

     Simultaneous Tests for General Linear Hypotheses

Multiple Comparisons of Means: Dunnett Contrasts


Fit: lm(formula = fo, data = mtcars)

Linear Hypotheses:
           Estimate Std. Error t value Pr(>|t|)    
4 - 3 == 0    8.427      1.823   4.621 0.000144 ***
5 - 3 == 0    5.273      2.431   2.169 0.072493 .  
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
(Adjusted p values reported -- single-step method)


     Simultaneous Tests for General Linear Hypotheses

Multiple Comparisons of Means: Dunnett Contrasts


Fit: lm(formula = fo, data = mtcars)

Linear Hypotheses:
           Estimate Std. Error t value Pr(>|t|)    
6 - 4 == 0   -6.921      1.558  -4.441 0.000235 ***
8 - 4 == 0  -11.564      1.299  -8.905 1.71e-09 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
(Adjusted p values reported -- single-step method)

The trick here is to note that the first argument to mcp is ... which usually means we can pass in a list of the form list(tag = value). We can’t specify tag as v here, so just create the list ll with a single element "Dunnett" and then change the names attribute of this list in the loop to be v. Then use do.call() to arrange to call mcp() with this argument list.

And for completeness, as @Josh metions in a comment above, from this answer from @Hadley the list can be more succinctly stated using the setNames() function:

for(v in xv){
  fo <- as.formula(paste("mpg",v,sep="~"))
  fit <- lm(fo,data=mtcars)
  print(summary(glht(fit, linfct = do.call(mcp, setNames(list("Dunnett"), v)))))
}