On Apr 19, 2011, at 3:46 AM, Michael Bach wrote:
Dear R Users,
Lets assume I have this data frame:
x y z
1 1.00 5 0.5
2 1.02 5 0.7
3 1.04 7 0.1
4 1.06 9 0.4
x and y columns are sorted and the values not necessarily integers. z
values are not sorted. Now I would like to create a matrix out of
this
with x as first column values and y as first row values. Matrix
element
a_11 shall be left NA. The a_ij should have the z value for the
corresponding x and y pair. The result shall be some sort of a grid
and
then e.g. look like:
[,1] [,2] [,3] [,4] [,5]
[1,] NA 5 6 7 9 (y)
[2,] 1.00 0.5 NA NA NA
[3,] 1.02 0.7 NA NA NA
[4,] 1.04 NA NA 0.1 NA
[5,] 1.06 NA NA NA 0.4
(x)
This example is just for illustration. The resulting matrix should
have
more numeric values than NA's.
I hope I made myself clear.
Perhaps but only if the third row of your example was incorrectly
constructed:
> dta <- rd.txt(" x y z
1 1.00 5 0.5
2 1.02 5 0.7
3 1.04 7 0.1
4 1.06 9 0.4")
#rd.txt() is a combo fn of read.table and textConnection
> mat <- matrix(NA, ncol=NROW(dta)+1, nrow=NROW(dta)+1)
> mat[2:NROW(mat),1] <- dta[["x"]]
> mat[1,2:NROW(mat)] <- dta[["y"]]
> diag(mat) <- c(NA, dta[["z"]])
> mat
[,1] [,2] [,3] [,4] [,5]
[1,] NA 5.0 5.0 7.0 9.0
[2,] 1.00 0.5 NA NA NA
[3,] 1.02 NA 0.7 NA NA
[4,] 1.04 NA NA 0.1 NA
[5,] 1.06 NA NA NA 0.4
Any hints on how to achieve this? Is there
already a function that does it? All searches I did pointed me to
data
type frame to matrix conversion...
David Winsemius, MD
West Hartford, CT
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