Hi:
Loop? We don't need no steeenking loop!! Here's a way to create a matrix
with matrix indexing that you can attach with x to create a new data frame.
Calling your original data frame df,
> m <- matrix(NA, nrow = nrow(df), ncol = 3)
# Create the indices of the initialized matrix to modify
> idx <- cbind(1:nrow(m), df$z)
# Map the modifications to the matrix
> m[idx] <- df$y
> m
[,1] [,2] [,3]
[1,] 13 NA NA
[2,] NA 8 NA
[3,] NA NA 7
[4,] 16 NA NA
[5,] NA 8 NA
[6,] NA NA 2
[7,] 11 NA NA
[8,] NA NA 9
data1 <- as.data.frame(cbind(df$x, m))
names(data1) <- c("x", "y1", "y2", "y3")
> data1
x y1 y2 y3
1 50 13 NA NA
2 14 NA 8 NA
3 3 NA NA 7
4 4 16 NA NA
5 6 NA 8 NA
6 10 NA NA 2
7 15 11 NA NA
8 14 NA NA 9
HTH,
Dennis
On Thu, Feb 25, 2010 at 5:17 AM, Juliet Ndukum <jpnts...@yahoo.com> wrote:
> I have a matrix, called data. I used the code below to rearrange the data
> such that the first column remains the same, but the y value falls under
> either columns 2, 3 or 4, depending on the value of z. If z=1 for example,
> then the value of y will fall under column 2, if z=2, the value of y falls
> under column 3, and so on.
>
> data
> x y z
> [1,] 50 13 1
> [2,] 14 8 2
> [3,] 3 7 3
> [4,] 4 16 1
> [5,] 6 8 2
> [6,] 10 2 3
> [7,] 15 11 1
> [8,] 14 9 3
> > data1 <- data.frame(matrix(0, length(x), ncol(data)+1))
> > colnames(data1) <- c("x","y1","y2","y3")
> > data1$x <- data[,1]
> > data1$y1 <- apply(data, 1, function(x) (ifelse(x[3]==1,x[2],NA)))
> > data1$y2 <- apply(data, 1, function(x) (ifelse(x[3]==2,x[2],NA)))
> > data1$y3 <- apply(data, 1, function(x) (ifelse(x[3]==3,x[2],NA)))
> > data1
> x y1 y2 y3
> 1 50 13 NA NA
> 2 14 NA 8 NA
> 3 3 NA NA 7
> 4 4 16 NA NA
> 5 6 NA 8 NA
> 6 10 NA NA 2
> 7 15 11 NA NA
> 8 14 NA NA 9
>
> I used the apply function (three times) to generate the output below, which
> is as I wish to have it.
> Can any one write for me a for loop that would produce the same results.
>
> Thanks in advance.
> JN
>
>
>
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>
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>
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