R help - Aug 2012 - apply function over same column of all objects in a list

Hello. Please forgive me if this problem has already been posted (and solved)
by someone else ... I can't find it anywhere though it seems so very basic.
Here it is:

I have a list comprised of several matrices, each of which has two columns.
> list
[[1]]
        [,1] [,2]
[1,]    1     3
[2,]    2     4

[[2]]
        [,1] [,2]
[1,]    5     7
[2,]    6     8

[[3]]
        [,1]   [,2]
[1,]    9      11
[2,]    10    12

I would like R to give me the highest value (max) of each matrice's 2nd
column, and also the max of all those individual highest values. I have
tried 

matrix.max <- for (i in 1:3) {
mapply ( max, list [[i]] [2] )
}

for each column's max and 

total.max <- for (i in 1:3) {
max(mapply ( max, list [[i]] [2] ))
}

for the total max, but neither works (result: NULL). What am I doing wrong?

 Thanks a lot,
Gail



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Thank you!!! But I realise I've simplified my data to the point that your
solution doesn't actually work -- not your fault, mine! My list is actually
more complicated than what I presented it to be; it's not composed of
numerical matrices but of lists, each being composed of 7 columns, the first
two of each (the ones that I am interested in, x and y) being numerical.
This is what my list really looks like (truncated):
> summary(mylist)
      Length Class   Mode
moh6  7      density list
moh7  7      density list
moh8  7      density list
...
etc.
> summary(mylist[[3]]) # I've taken number 3 as an example, but
they're all
> the same
          Length Class  Mode     
x         512    -none- numeric  
y         512    -none- numeric  
bw          1    -none- numeric  
n           1    -none- numeric  
call        2    -none- call     
data.name   1    -none- character
has.na      1    -none- logical  

Any suggestion how to get the max of column y for each sub-list (moh6, moh7,
moh8 etc.), and to the max of all these individual maxes? By the way,

lapply(list1,FUN=function(x)x[,2][which.max(x[,2])])

gives me the individual maxes (for a list composed of numerical matrices),
but how do I get to the overall max?

Many thanks ...



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On Wed, Aug 1, 2012 at 8:43 AM, gail <ortoga-r at yahoo.de>
wrote:
> Hello. Please forgive me if this problem has already been posted (and
solved)
> by someone else ... I can't find it anywhere though it seems so very
basic.
> Here it is:
>
> I have a list comprised of several matrices, each of which has two columns.
>
>> list
> [[1]]
>         [,1] [,2]
> [1,]    1     3
> [2,]    2     4
>
> [[2]]
>         [,1] [,2]
> [1,]    5     7
> [2,]    6     8
>
> [[3]]
>         [,1]   [,2]
> [1,]    9      11
> [2,]    10    12
>
> I would like R to give me the highest value (max) of each matrice's 2nd
> column, and also the max of all those individual highest values. I have
> tried
>
> matrix.max <- for (i in 1:3) {
> mapply ( max, list [[i]] [2] )
> }
>
> for each column's max and
>
> total.max <- for (i in 1:3) {
> max(mapply ( max, list [[i]] [2] ))
> }
>
I think what you just want is to put the "get second column" part
within the function that you apply() [Actually lapply() since you have
a list] -- to put it another way, note that "get the second column"
can be considered part of the operation you perform on each list
element, rather than defining the thing to which you apply the max()
function.

Something like this results:

lapply(list, function(x) max(x[,2]))

This will go over the list and apply the function "get the max of the
second column"

Best,
Michael
> for the total max, but neither works (result: NULL). What am I doing wrong?
>
>  Thanks a lot,
> Gail
>
>
>
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> View this message in context:
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>
> ______________________________________________
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

HI,
I tested the code for another set of data with added complexity.  Seems to
be working fine.
list1<-list(data.frame(x=1:6,y=c(4,5,3,2,1,8),bw=c(4,18,12,3,4,9)))
list2<-list(data.frame(x=c(1,2,18,16,15),y=c(4,5,9,2,1),bw=c(4,18,22,3,4)))
list3<-list(data.frame(x=c(4,6,9),y=c(8,24,12),bw=c(14,31,36)))
list4<-list(list1,list2,list3)
#individual cases
lapply(list4[[1]][[1]],FUN=function(x) x[which.max(x)])
lapply(list4[[2]][[1]],FUN=function(x) x[which.max(x)])
 lapply(list4[[3]][[1]],FUN=function(x) x[which.max(x)])

#Whole set
flatlist <- function(mylist){
   lapply(rapply(mylist, enquote, how="unlist"), eval)
 }
 list5<-flatlist(list4)
dat6<-data.frame(key=names(list5),dat5)
 dat6
aggregate(value~key,data=dat6,max)
  #key value
#1  bw    36
#2   x    18
#3   y    24
A.K. 




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Arun, I see you've defined dat5 in your later message; however the same
applies as to the above: the code doesn't work if the list contains
non-numerical elements.
Gail



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