[R] apply diff type function to matrix

[David L Carlson]

I'm not sure we have enough information, but given your matrix:

> mt <- matrix(c(1, 2, 3, 10, 15, 20, 20, 40, 80, 30, 60, 120), 3, 4)
> mt
     [,1] [,2] [,3] [,4]
[1,]    1   10   20   30
[2,]    2   15   40   60
[3,]    3   20   80  120
# Get differences between adjacent values in each column
> mt.d <- abs(diff(mt))
> mt.d
     [,1] [,2] [,3] [,4]
[1,]    1    5   20   30
[2,]    1    5   40   60
# Get ratio of cols 2-4 to col 1
> mt.d[,-1]/mt.d[,1]
     [,1] [,2] [,3]
[1,]    5   20   30
[2,]    5   40   60
# Get ratio of cols 2-4 to cols 1-3
> mt.d[,-1]/mt.d[,1:3]
     [,1] [,2] [,3]
[1,]    5    4  1.5
[2,]    5    8  1.5

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of message
Sent: Thursday, June 19, 2014 8:42 AM
To: r-help at r-project.org
Subject: [R] apply diff type function to matrix

Readers,

For a matrix:
1 10 20 30
2 15 40 60
3 20 80 120

Using a spreadsheet, a differential function can be applied to the data 
as a formula:
|(10-15)/(1-2)| ... repeated for each pair of adjacent values
What is the corresponding function in R please?
Is it better to write a new function, or to use some form of function 
'diff'?

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