[R] how to loop thru a matrix or data frame , and append calculations to a new data frame?

[John Kane]

Duh, thought of that after I'd left for dinner :(

--- On Sat, 10/31/09, David Winsemius <dwinsemius at comcast.net> wrote:

> From: David Winsemius <dwinsemius at comcast.net>
> Subject: Re: [R] how to loop thru a matrix or data frame , and append calculations to  a new data frame?
> To: "John Kane" <jrkrideau at yahoo.ca>
> Cc: r-help at r-project.org, "Robert Wilkins" <robstdev at gmail.com>
> Received: Saturday, October 31, 2009, 2:00 PM
> On Oct 31, 2009, at 12:33 PM, John
> Kane wrote:
> 
> > Do you mean to apply the same calculation to each
> element?
> > 
> > ? apply
> > 
> > mydata  <- data.frame(aa = 1:5, bb= 11:15)
> > mp5 <- function(x) x*5
> > mp5data <-  apply(mydata, 2, mp5)
> > mp5data
> 
> It would have been much more compact (and in the spirit of
> functional programming) to just do:
> 
> mp5data <- mydata*5
> # binary operations applied to dataframes give sensible
> results when the data types allow.
> mp5data
>      aa bb
> [1,]  5 55
> [2,] 10 60
> [3,] 15 65
> [4,] 20 70
> [5,] 25 75
> 
> Many times the loops are implicit in the vectorized design
> of R. And that solution would not result in the structure
> requested, for which some further "straightening" would be
> needed:
> 
> > mp5data <- as.vector(as.matrix(mydata)*5)
> > mp5data
>  [1]  5 10 15 20 25 55 60 65 70 75
> 
> -- David
> > 
> > This is functionally equivelent to a double if loop.
> > 
> > mydata  <- data.frame(aa = 1:5, bb= 11:15)
> > newdata <- data.frame(matrix(rep(NA,10), nrow=5))
> > 
> > for (i in 1:length(mydata[1,])) {
> >  for (j in 1:5) {
> >    newdata[j,i] <- mydata[j,i]*5
> > }
> >    }
> > 
> > newdata
> > 
> > 
> > 
> > --- On Fri, 10/30/09, Robert Wilkins <robstdev at gmail.com>
> wrote:
> > 
> >> From: Robert Wilkins <robstdev at gmail.com>
> >> Subject: [R] how to loop thru a matrix or data
> frame , and append calculations to  a new data frame?
> >> To: r-help at r-project.org
> >> Received: Friday, October 30, 2009, 11:46 AM
> >> How do you do a double loop through a
> >> matrix or data frame , and
> >> within each iteration , do a calculation and
> append it to a
> >> new,
> >> second data frame?
> >> (So, if your original matrix or data frame is 4 x
> 5 , then
> >> 20
> >> calculations are done, and the new data frame,
> which had 0
> >> rows to
> >> start with, now has 20 rows)
> >> 
> >> ______________________________________________
> >> 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.
> >> 
> > 
> > ______________________________________________
> > 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.
> 
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
> 
> 


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