Changing selected elements of an array

Hi!

I have a matrix defined on geographical positions (through) row and column
names. I need to change a number of elements in this matrix using the
information of a data.frame containing geographical positions and a number of
variables.

Changing the value of one specific element is easy, but changing on a number
of selected positions seems more difficult. When I use the geographical
positions of the data.frame as index, blobs are changed and not individual
elements.

How can I circumvent this feature of R?

E.g: in this situation I would like the downward diagonal to be changed, not
the square box...

tmpmat <-

matrix(NA,nrow=9,ncol=10,dimnames=list(formatC(tmplat,format="f",digits=2),formatC(tmplon,format="f",digits=2)))

tmpmat

? ? ?8.00 9.50 9.75 14.25 15.00 15.75 18.00 20.50 21.75 25.25
55.25 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
56.75 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
57.75 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
58.00 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
59.50 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
62.75 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
64.50 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
66.25 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
67.25 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA

tmpmat[c("58.00","59.50","62.75"),c("15.00","15.75","18.00")] <- 300
tmpmat

? ? ?8.00 9.50 9.75 14.25 15.00 15.75 18.00 20.50 21.75 25.25
55.25 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
56.75 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
57.75 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
58.00 ? NA ? NA ? NA ? ?NA ? 300 ? 300 ? 300 ? ?NA ? ?NA ? ?NA
59.50 ? NA ? NA ? NA ? ?NA ? 300 ? 300 ? 300 ? ?NA ? ?NA ? ?NA
62.75 ? NA ? NA ? NA ? ?NA ? 300 ? 300 ? 300 ? ?NA ? ?NA ? ?NA
64.50 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
66.25 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
67.25 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA

While I wanted:

tmpmat

? ? ?8.00 9.50 9.75 14.25 15.00 15.75 18.00 20.50 21.75 25.25
55.25 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
56.75 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
57.75 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
58.00 ? NA ? NA ? NA ? ?NA ? 300 ? ?NA ? NA ? ?NA ? ?NA ? ?NA
59.50 ? NA ? NA ? NA ? ?NA ? ?NA ? 300 ? NA ? ?NA ? ?NA ? ?NA
62.75 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? 300 ? ?NA ? ?NA ? ?NA
64.50 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
66.25 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA
67.25 ? NA ? NA ? NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA ? ?NA

All the best
?ystein
--
Dr. Oystein Godoy
Norwegian Meteorological Institute
P.O.BOX 43, Blindern, N-0313 OSLO, Norway
Ph: (+47) 2296 3000 (switchb) 2296 3334 (direct line)
Fax:(+47) 2296 3050 Institute home page: http://met.no/

You can do it by passing a matrix for indexing instead of two vectors.
 Here's an example:

tmpmat <- matrix(NA, nrow = 10, ncol = 10,
  dimnames = list(letters[1:10], LETTERS[1:10]))

tmpmat[cbind(c("d", "e", "f"), c("D", "E", "F"))] <- 100
tmpmat

The matrix is created using cbind() to columnwise bind the two vectors
together.  Then it does what you want I think.

Hope this helps,

Hi Joshua,

Many thanks for your quick reply.

You can do it by passing a matrix for indexing instead of two vectors.
?Here's an example:

tmpmat <- matrix(NA, nrow = 10, ncol = 10,
? dimnames = list(letters[1:10], LETTERS[1:10]))

tmpmat[cbind(c("d", "e", "f"), c("D", "E", "F"))] <- 100
tmpmat

The matrix is created using cbind() to columnwise bind the two vectors
together. ?Then it does what you want I think.

Hope this helps,

This looks interesting and is what I want, but I am not fully understanding
the output I receive. The input array has 100 elements while the resulting
vector after replacement is 106 elements long. I have tried to understand the
manual on this, but it is yet not obvious for me how I am supposed to handle
this output.

All the best
?ystein
--
Dr. Oystein Godoy
Norwegian Meteorological Institute
P.O.BOX 43, Blindern, N-0313 OSLO, Norway
Ph: (+47) 2296 3000 (switchb) 2296 3334 (direct line)
Fax:(+47) 2296 3050 Institute home page: http://met.no/

This looks interesting and is what I want, but I am not fully
understanding the output I receive. The input array has 100 elements
while the resulting vector after replacement is 106 elements long. I
have tried to understand the manual on this, but it is yet not obvious
for me how I am supposed to handle this output.

I cannot reproduce this behavior.  On my system, the output has 100
elements.