[R] recommended way to group function calls in Sweave

[Liviu Andronic]

Dear all
When using Sweave, I'm always hitting the same bump: I want to group
repetitive calls in a function, but I want both the results and the
function calls in the printed output. Let me explain myself.

Consider the following computation in an Sweave document:
summary(iris[,1:2])
cor(iris[,1:2])

When using these two calls directly, I obtain the following output:
> summary(iris[,1:2])
  Sepal.Length    Sepal.Width
 Min.   :4.300   Min.   :2.000
 1st Qu.:5.100   1st Qu.:2.800
 Median :5.800   Median :3.000
 Mean   :5.843   Mean   :3.057
 3rd Qu.:6.400   3rd Qu.:3.300
 Max.   :7.900   Max.   :4.400
> cor(iris[,1:2])
             Sepal.Length Sepal.Width
Sepal.Length    1.0000000  -0.1175698
Sepal.Width    -0.1175698   1.0000000


However, if I try to group the calls in a function:
f <- function(d, ind){
  print(summary(d[ , ind]))
  print(cor(d[ , ind]))
  return(invisible(NULL))
}


Then I get a different output in the Sweave PDF:
> f(iris, 1:2)
  Sepal.Length    Sepal.Width
 Min.   :4.300   Min.   :2.000
 1st Qu.:5.100   1st Qu.:2.800
 Median :5.800   Median :3.000
 Mean   :5.843   Mean   :3.057
 3rd Qu.:6.400   3rd Qu.:3.300
 Max.   :7.900   Max.   :4.400
             Sepal.Length Sepal.Width
Sepal.Length    1.0000000  -0.1175698
Sepal.Width    -0.1175698   1.0000000


Of course I can use 'echo=F' to remove the '> f(iris, 1:2)' in the
above, but how can I do to keep the original calls 'summary(d[ ,
ind])' and 'cor(d[ , ind])'? Or even better, could the actual calls be
used, after the replacement of arguments by their values:
'summary(iris[,1:2])' and 'cor(iris[,1:2])'.

Or is the recommended way to use cat()-ed statements:
f <- function(d, ind){
  cat('Variable summary:\n')
  print(summary(d[ , ind]))
  cat('\nCorrelation table:\n')
  print(cor(d[ , ind]))
  return(invisible(NULL))
}


To obtain such output:
> f(iris, 1:2)
Variable summary:
  Sepal.Length    Sepal.Width
 Min.   :4.300   Min.   :2.000
 1st Qu.:5.100   1st Qu.:2.800
 Median :5.800   Median :3.000
 Mean   :5.843   Mean   :3.057
 3rd Qu.:6.400   3rd Qu.:3.300
 Max.   :7.900   Max.   :4.400

Correlation table:
             Sepal.Length Sepal.Width
Sepal.Length    1.0000000  -0.1175698
Sepal.Width    -0.1175698   1.0000000


What is the recommended way of grouping repetitive function calls?
What do you usually use in your own documents? Regards
Liviu


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