[R] Regular repeats

[arun]

Hi,
You could try:
set.seed(24)
  dat1<- as.data.frame(matrix(sample(1:50,29*6,replace=TRUE),ncol=6))

((seq_len(nrow(dat1))-1)%/%6)+1
# [1] 1 1 1 1 1 1 2 2 2 2 2 2 3 3 3 3 3 3 4 4 4 4 4 4 5 5 5 5 5


#For a particular column:
aggregate(dat1[,5],list(((seq_len(nrow(dat1))-1)%/%6)+1),FUN=mean)
#  Group.1        x
#1       1 38.16667
#2       2 29.50000
#3       3 23.16667
#4       4 21.16667
#5       5 20.60000
#or for the whole columns

aggregate(dat1,list(((seq_len(nrow(dat1))-1)%/%6)+1),FUN=mean)
#  Group.1       V1       V2       V3       V4       V5       V6
#1       1 28.33333 17.50000 12.66667 35.00000 38.16667 30.16667
#2       2 26.16667 31.33333 35.33333 19.66667 29.50000 24.83333
#3       3 24.00000 11.83333 20.00000 25.50000 23.16667 20.83333
#4       4 18.33333 23.33333 23.66667 20.33333 21.16667 21.16667
#5       5 22.60000 30.40000 17.40000 21.80000 20.60000 24.40000

#or

library(plyr)
res1<-ddply(dat1,.(((seq_len(nrow(dat1))-1)%/%6)+1),summarize,MeanV1=mean(V1)) 
 colnames(res1)[1]<-"Group"
res1
#  Group   MeanV1
#1     1 28.33333
#2     2 26.16667
#3     3 24.00000
#4     4 18.33333
#5     5 22.60000
A.K.





----- Original Message -----
From: jsf1982 <jamie.freeman at ucl.ac.uk>
To: r-help at r-project.org
Cc: 
Sent: Tuesday, August 13, 2013 12:46 PM
Subject: [R] Regular repeats

Hi,
Many apologies for the simplicity (hopefully!) of this request - I can't
find it on the forum, but it may have been asked in the past.

I have a data frame consisting of ~2000 rows. I simply want to take the
average of the first 6, then the next 6, then the next 6 until the end of
the table. 
The command 

mean(mole[1:6,c("PercentPI")])

gets me the first 6 rows (column is PercentPI), but I don't know how to
increase the rows incrementally.

Thanks in advance.
J





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