[R] gridding values in a data frame
jdeisenberg
catcode at catcode.com
Fri May 1 00:06:16 CEST 2009
dxc13 wrote:
>
> Hi all,
> I have a data frame that looks like such:
> LATITUDE LONGITUDE TEMPERATURE TIME
> 36.73 -176.43 58.32 1
>
> and this goes on for a A LOT more records, until time=1200
>
> I want to create a 5 degree by 5 degree grid of this data, with the value
> of temperature in the appropriate grid cell. I want one grid for each
> time value.
>
> dxc13
>
The following appears to work, but is most definitely *not* in the "spirit
of R" -- it's more like a C program written in R. Undoubtedly someone will
come up with a much more clever method. (This is always my problem; I come
up with a workable solution, but it's not elegant.)
Note: the grid has to have 37 rows, since latitude -90 to +90 (inclusive)
takes 37 5-degree increments; since -180 and +180 longitude are the same,
you would never have them as separate numbers.
d <- read.csv("weather.csv")
for (i in 1:1200)
{
x <- d[d$TIME==i,]
if (length(x$TIME) > 0)
{
print(sprintf("# of elements for time %d: %d", i,
length(x$TIME)))
grid <- matrix(NA, nrow=37, ncol=72)
for (j in 1:length(x$TIME))
{
lat <- 1 + trunc((90 + x$LATITUDE[j]) / 5)
long <- 1 + trunc((180 + x$LONGITUDE[j]) / 5)
grid[lat,long] <- x$TEMPERATURE[j]
}
write(t(grid), file=sprintf("time%d.csv", i), ncolumns=72, sep=",")
}
}
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