[R] For loop by factor.

[jim holtman]

try this:

>  test <- data.frame(A=c("a", "a", "a", "b", "b", "c", "c", "c", "c"), B=c(3,2,1,3,2,2,3,1,1))
>  test
  A B
1 a 3
2 a 2
3 a 1
4 b 3
5 b 2
6 c 2
7 c 3
8 c 1
9 c 1
>  # determine which group is not decreasing
>  tapply(test$B, test$A, function(x) any(diff(x) > 0))
    a     b     c
FALSE FALSE  TRUE
>


On Sun, Jun 19, 2011 at 4:20 PM, Christopher Peters <cpeter9 at lsu.edu> wrote:
> I have a data.frame as follows:
>
> a  3
> a  2
> a  1
> b  3
> b  2
> c  2
> c  3
> c  1
> c  1
>
> Each factor (a, b, c) should be monotonically decreasing, notice that factor
> 'c' is not.
>
> I could use some help to figure out how to form a logical structure (mostly
> just syntax), that will check each 'next value' for each factor to see if it
> is less than the previous value.  If it is less than the previous value, do
> nothing, else subtract 'next value' from 'current value', add that amount to
> the starting value and each previous value to the 'next value' is greater
> than 'previous value'.
>
> So basically the data.frame would look like:
>
> a 3
> a 2
> a 1
> b 3
> b 2
> c 3
> c 3
> c 1
> c 1
>
> Thanks for your help!
> __________________________________
> Christopher P. Peters
> Research Associate
> Center for Energy Studies
> http://www.enrg.lsu.edu/staff/peters
> Energy, Coast & Environment Building
> Louisiana State University
> Baton Rouge, LA 70803
> Telephone: 225-578-4400
> Fax: 225-578-4541
>
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>
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>



-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?