[R] how to calculate the mean of a group in a table

[Pete Brecknock]

tornanddesperate wrote:
> 
> Hi its me again
> 
> I don't mean to get on your nerves, but the use of R proofs to be a bit
> more complicated than envisaged.
> 
> I would like to calculate the mean of a group of values, here
> "wage_accepted". The group is determined by the stage and period, so in
> the end there should be a column with the values of the wages in period 1
> stage1, period 1 stage 2, period 2 stage1... Unfortunately, I haven't much
> of a clue on how to program this. Could you tell me how the function
> should roughly look like – if-else, loops included or not – in the end ?
> 

A couple of possible approaches ....

# read in your data
lines <-"treatment session period stage wage_accepted type
1       1      1     1            25  low
1       1      1     1            19  low
1       1      1     1            15  low
1       1      1     2            32 high
1       1      1     2            13  low
1       1      1     2            14  low
1       1      2     1            17  low
1       1      2     1            12  low"

d <- read.table(textConnection(lines), header = TRUE)
closeAllConnections()

# 1. using the aggregate function
aggregate(d$wage_accepted, list(period=d$period, stage=d$stage), FUN=mean)

# 2. using the by function
by(d$wage_accepted,list(d$period,d$stage),FUN=mean)

As for tutorial resources, I would recommend visiting CRAN at
http://cran.r-project.org/ ... follow the "Manuals" link on the left hand
side of the page. 

HTH

Pete 
 

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