Re: [R] Howto build combinations of colums of a data frame

David Winsemius Thu, 16 Apr 2009 10:30:56 -0700

Those are not actually dataframes. They are matrices. If you want tomake them into dataframes, use a coercive function. The names can begenerated from the original column names using the same constructionas the column creation:


> apply(combn(colnames(DF),2), 2, paste, collapse="*")
[1] "a*b" "a*c" "a*d" "b*c" "b*d" "c*d"
> apply(combn(colnames(DF),3), 2, paste, collapse="*")
[1] "a*b*c" "a*b*d" "a*c*d" "b*c*d"


--
David


On Apr 16, 2009, at 12:33 PM, Juergen Rose wrote:

Am Donnerstag, den 16.04.2009, 10:59 -0400 schrieb David Winsemius:

Thanks David,

is there also a shorter way to get the columns names of the new data
frames?

Juergen

On Apr 16, 2009, at 10:14 AM, Juergen Rose wrote:

Hi,

as a R-newcomer I would like to create some new data frames from a
given
data frame. The first new data frame should content all pairs of the
columns of the original data frame. The second new data frame should
content all tripels of of the columns of the original data frame and
the
last the quadrupel of columns. The values in the new data frames
should
be the product of two, three our four original single field values.
For
pairs and tripels I could realize that task, with the following R
script:

Lines <- "a    b    c    d
  13     0    15   16
  23    24    25    0
  33    34     0   36
   0    44    45   46
  53    54     0   55"

DF <- read.table(textConnection(Lines), header = TRUE)

nrow <-length(rownames(DF))
cnames <- colnames(DF)
nc <-length(DF)

nc.pairs <- nc*(nc-1)/2
#  initialize vector
cnames.new <- c(rep("",nc.pairs))
ind <- 1
print(sprintf("nc=%d",nc))
for (i in 1:(nc-1)) {
if (i+1 <= nc ) {
  for (j in (i+1):nc) {
    cnames.new[ind] <- paste(cnames[i],cnames[j],sep="")
    ind <- ind+1
  }
}
}

ind <- 1
#  initialize data.frame
pairs <- data.frame(matrix(c(rep(0,nc.pairs*nrow)),ncol=nc.pairs))
for (i in 1:nc) {
if (i+1 <= nc ) {
  for (j in (i+1):nc) {
    t <- DF[,i] * DF[,j]
    pairs[[ind]] <- t
    ind <- ind+1
  }
}
}
colnames(pairs) <- cnames.new
print("pairs=");   print(pairs)


apply(combn(colnames(DF),2), 2, function(x) DF[,x[1]]*DF[,x[2]] )
     [,1] [,2] [,3] [,4] [,5] [,6]
[1,]    0  195  208    0    0  240
[2,]  552  575    0  600    0    0
[3,] 1122    0 1188    0 1224    0
[4,]    0    0    0 1980 2024 2070
[5,] 2862    0 2915    0 2970    0



nc.tripels <- nc*(nc-1)*(nc-2)/6
#  initialize vector
cnames.new <- c(rep("",nc.tripels))
ind <- 1
print(sprintf("nc=%d",nc))
for (i in 1:nc) {
if (i+1 <= nc ) {
  for (j in (i+1):nc) {
    if (j+1 <= nc ) {
      for (k in (j+1):nc) {
        cnames.new[ind] <-
paste(cnames[i],cnames[j],cnames[k],sep="")
        ind <- ind+1
      }
    }
  }
}
}

ind <- 1
#  initialize data.frame
tripels <-
data.frame(matrix(c(rep(0,nc.tripels*nrow)),ncol=nc.tripels))
for (i in 1:(nc-1)) {
if (i+1 <= nc ) {
  for (j in (i+1):nc) {
    if (j+1 <= nc ) {
      for (k in (j+1):nc) {
        t <- DF[,i] * DF[,j] * DF[,k]
        tripels[[ind]] <- t
        ind <- ind+1
      }
    }
  }
}
}
colnames(tripels) <-  cnames.new
print("tripels=");   print(tripels)

apply(combn(colnames(DF),3), 2, function(x)

DF[,x[1]]*DF[,x[2]]*DF[,x[3]])
      [,1]   [,2] [,3]  [,4]
[1,]     0      0 3120     0
[2,] 13800      0    0     0
[3,]     0  40392    0     0
[4,]     0      0    0 91080
[5,]     0 157410    0     0


David Winsemius, MD
Heritage Laboratories
West Hartford, CT

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Re: [R] Howto build combinations of colums of a data frame

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