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Christopher Peters

2011-Jun-19 20:20 UTC

[R] For loop by factor.

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

	[[alternative HTML version deleted]]

Sarah Goslee

2011-Jun-19 23:02 UTC

head link

[R] For loop by factor.

This works, but I'm still hunting for a more elegant final
step:> 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))
> test2 <- lapply(split(test$B, test$A), sort, dec=TRUE)
> test3 <- data.frame(A=rep(names(test2), times=lapply(test2, length)),
B=unlist(test2))
It will also group data by factor, which was already done in your example.

Sarah

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
>-- 
Sarah Goslee
http://www.functionaldiversity.org

jim holtman

2011-Jun-20 00:14 UTC

head link

[R] For loop by factor.

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
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?

Bill.Venables at csiro.au

2011-Jun-20 00:15 UTC

head link

[R] For loop by factor.

If I understand you correctly, you are trying to find the cumulative maximum
from the end within each level of the factor.  If this is what you are trying to
do, then here is one way you might like to do it.  First, define the function:
> cumMax <- function(x) Reduce(max, x, right = TRUE, accumulate = TRUE)
Here is how you might use it:
> 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> (test <- within(test, B <- ave(B, A, FUN = cumMax))  A B
1 a 3
2 a 2
3 a 1
4 b 3
5 b 2
6 c 3
7 c 3
8 c 1
9 c 1 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Christopher Peters
Sent: Monday, 20 June 2011 6:21 AM
To: r-help at r-project.org
Subject: [R] For loop by factor.

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

	[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Sarah Goslee

2011-Jun-20 14:14 UTC

head link

[R] For loop by factor.

Chris,

This doesn't cover all possible cases, but does work for your example.
It should be enough for you to tweak for your actual data.

diffsum <- function(x) {
	# first identify the decreasing values
	# and the difference between increasing values
	xdif <- x[2:length(x)] - x[1:(length(x)-1)]
	xdif <- c(xdif, 0) # last element has nothing to compare to
	xdif[xdif <= 0] <- 0
	# then figure out what to add
	# NOTE: your example is not clear on what to do if
	# there's a gap followed by more increasing number
	xsum <- rev(cumsum(rev(xdif)))
	xsum[xdif == 0] <- 0
	x + xsum
}


diffsum(c(2,3,5,2,1))


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))
test2 <- lapply(split(test$B, test$A), diffsum)
test3 <- data.frame(A=rep(names(test2), times=lapply(test2, length)),
B=unlist(test2))

Sarah

On Mon, Jun 20, 2011 at 9:51 AM, Christopher Peters <cpeter9 at lsu.edu>
wrote:> Sarah, ?thank you this is very close.
> The difference is that I'm not trying to sort to make it monotonic, but
> rather take the difference between any increasing value in the series and
> the previous value and add that difference back into each previous value.
> For example.
> column ? var1 ? ?diff (0 where decreasing) ? ?var2 (<--correct)
> a ? ? ? ? ? ? 2 ? ? ? ?1 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?5 <- (2 +
> (1+2))
> a ? ? ? ? ? ? 3 ? ? ? ?2 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?5 <- (3 +
(2))
> a ? ? ? ? ? ? 5 ? ? ? ?0 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?5
> a ? ? ? ? ? ? 2 ? ? ? ?0 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?2
> a ? ? ? ? ? ? 1 ? ? ? ?0 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?1
> Chris
> ______________________
>
>
> On Sun, Jun 19, 2011 at 6:02 PM, Sarah Goslee <sarah.goslee at
gmail.com>
> wrote:
>>
>> This works, but I'm still hunting for a more elegant final step:
>> > 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))
>> > test2 <- lapply(split(test$B, test$A), sort, dec=TRUE)
>> > test3 <- data.frame(A=rep(names(test2), times=lapply(test2,
length)),
>> > B=unlist(test2))
>>
>> It will also group data by factor, which was already done in your
example.
>>
>> Sarah
>>
>> 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
>> >
>> --

-- 
Sarah Goslee
http://www.functionaldiversity.org

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