Aggregate data to lower resolution

Dear Jean,

Greetings of the new year. Hope you are doing well.

I apologise for writing to you off-list but this might be a really silly
question and I wanted to clarify without bothering everyone. Would kindly
help me out? Hope this is not too much of a bother.

My original question was regarding aggregating data to 1 degree x 1
degree. You had kindly provided the following solution:

temp$long1 <- floor(temp$longitude)
temp$lat1 <- floor(temp$latitude)
temp1 <- aggregate(GDP ~ long1 + lat1, temp, mean)

Everything works well, my only question (and confusion) is that for
aggregating from 0.5 degree by 0.5 degree to 1 degree by 1 degree, should
we use sum instead of mean?

temp1 <- aggregate(GDP ~ long1 + lat1, temp, sum)

I really hope I'm not bothering you too much. Thanks again.

Sincerely,

Milu

On Fri, Jul 22, 2016 at 3:06 PM, Adams, Jean <jvadams at usgs.gov> wrote:

Milu,

Perhaps an approach like this would work.  In the example below, I
calculate the mean GDP for each 1 degree by 1 degree.

temp$long1 <- floor(temp$longitude)
temp$lat1 <- floor(temp$latitude)
temp1 <- aggregate(GDP ~ long1 + lat1, temp, mean)

  long1 lat1        GDP
1   -69  -55 0.90268640
2   -68  -55 0.09831317
3   -72  -54 0.22379000
4   -71  -54 0.14067290
5   -70  -54 0.00300380
6   -69  -54 0.00574220

Jean

On Thu, Jul 21, 2016 at 3:57 PM, Miluji Sb <milujisb at gmail.com> wrote:

Dear all,

I have the following GDP data by latitude and longitude at 0.5 degree by
0.5 degree.

temp <- dput(head(ptsDF,10))
structure(list(longitude = c(-68.25, -67.75, -67.25, -68.25,
-67.75, -67.25, -71.25, -70.75, -69.25, -68.75), latitude = c(-54.75,
-54.75, -54.75, -54.25, -54.25, -54.25, -53.75, -53.75, -53.75,
-53.75), GDP = c(1.683046, 0.3212307, 0.0486207, 0.1223268, 0.0171909,
0.0062104, 0.22379, 0.1406729, 0.0030038, 0.0057422)), .Names =
c("longitude",
"latitude", "GDP"), row.names = c(4L, 17L, 30L, 43L, 56L, 69L,
82L, 95L, 108L, 121L), class = "data.frame")

I would like to aggregate the data 1 degree by 1 degree. I understand
that
the first step is to convert to raster. I have tried:

rasterDF <- rasterFromXYZ(temp)
r <- aggregate(rasterDF,fact=2, fun=sum)

But this does not seem to work. Could anyone help me out please? Thank
you
in advance.

Sincerely,

Milu

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