[R] Using functions/loops for repetitive commands

[Gerrit Eichner]

Hello, Derek,

see below.

On Thu, 5 May 2011, dereksloan wrote:

> I still need to do some repetitive statistical analysis on some outcomes 
> from a dataset.
>
> Take the following as an example;
>
> id	sex	hiv	age	famsize	bmi	resprate
> 1	M	Pos	23	2	        16	15
> 2	F	Neg	24	5	        18	14
> 3	F	Pos	56	14	        23	24
> 4	F	Pos	67	3	        33	31
> 5	M	Neg	34	2	        21	23
>
> I want to know if there are statistically detectable differences in all 
> of the continuous variables in my data set when subdivided by sex or hiv 
> status (ie are age, family size, bmi and resprate different in my male 
> and female patients or in hiv pos/neg patients) Of course I can use 
> wilcoxon or t-tests e.g:
>
> wilcox.test( age~sex)
> wilcox.test(famsize~sex)
> wilcox.test(bmi~sex)
> wilcox.test(resprate~sex)
> wilcox.test( age~hiv)
> wilcox.test(famsize~hiv)
> wilcox.test(bmi~hiv)
> wilcox.test(resprate~hiv)
> .... [snip]


Define, e. g.,

my.wilcox.tests <- function( var.names, groupvar.name, data) {
  lapply( var.names,
          function( v) {
           form <- as.formula( paste( v, "~", groupvar.name))
           wilcox.test( form, data = data)
           } )
  }


and call something like

my.wilcox.test( <character vector with relevant variable names>,
                 <character string with relevant grouping variable>,
                 data = <your data set as data frame>)

Caveat: untested!

  Hth  --  Gerrit

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Dr. Gerrit Eichner                   Mathematical Institute, Room 212
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