# [R] to divide column cells by the mean of another column

arun smartpink111 at yahoo.com
Sun Apr 20 17:30:17 CEST 2014

```Hi,

May be this helps:
fun1 <- function(beginColumn, by, data) {
indx <- seq(beginColumn, ncol(data), by = by)
dataNew <- data[, indx[1]:ncol(data)]
indx1 <- cumsum(seq(ncol(data)) %in% indx)
indx2 <- indx1[indx1 != 0]
lst1 <- lapply(split(seq_along(indx2), indx2), function(i) {
x1 <- dataNew[, i, drop = FALSE]
if (ncol(x1) > 1) {
x1[, -1]/mean(x1[, 1])
}
})
res <- data.frame(lst1[sapply(lst1, length) > 0])
colnames(res) <- gsub(".*\\.", "", colnames(res))
res
}

set.seed(458)
dat1 <- as.data.frame(matrix(sample(5,10*5,replace=TRUE),ncol=10))

set.seed(34)
dat2 <- as.data.frame(matrix(sample(20,21*5,replace=TRUE),ncol=21))
fun1(2,4,dat1)
fun1(2,5,dat2)

A.K.

On Sunday, April 20, 2014 5:55 AM, Andre Zacharia <andre.zacharia at gmail.com> wrote:
Dear all,

I am getting data columnwise that I need to divide by the mean of another
column

If the column is the previous one this code works perfectly well:

fun1 <- function(beginColumn, by, data) { indx <- seq(beginColumn,
ncol(data), by = by) as.data.frame(t(100 - (t(data[, indx])/colMeans(data[,
indx - 1], na.rm = TRUE)) *  100))
}
(Arun helped me with this code, thank you again!...)

But, the things is now more complicated...

I need to program a function that allow me to divide for example cells from
column 3 on mean from column 2 and cells from column 4 on mean of column 2
and the 5 etc. Then column 6 is another column from whch I  need to extract
the mean and to do the same with column 7 and 8, etc...

so if  I have:

1  2  3 4  1  5
2  5  4 7  2  8
3  4  5 9  3  7
4  7  7 9  4  3

The serie 1,2,3,4 ar just enumerating so not useful at this timepoint.

the results should be (from excel...):
4,5 33,3333333 11,1111111 -11,1111111   11,1111111 -55,5555556 -77,7777778
-11,1111111 -100 -55,5555556   -55,5555556 -100
33,3333333
I tried to work on modyfying indx-1 by 2*indx-2, but this is not doing the
job... I tried many other things so that I am now stucked.

Does Anyone has a brilliant idea?

Many many thanks

André ZACHARIA

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