R help - Aug 2011 - apply function to spatial grid data frame to calculate CTI

Dear R helpers,
I'm new to R and struggling with applying functions to a spatial grid data
frame, called data for example.data has a variable named "slope" and
"uparea"
Basically, I need to calculate the tan(data$slope)Next, I need to divide
data$uparea by data$slope and take the log() of that all
In the basic examples I found how to make simple multiplications with a scalar
likedata[["slope"]] = data[["slope"]]/2 # assigns new
attribute
I come from a background in GIS and fortran, so used to dealing with ordinary
matrices, I'll admit I'm having trouble with understanding the format of
this spatial grid data frame structureI've been trying different methods to
index the data frame, or working with the function "lapply" but so far
I can't seem to get my head wrapped around it.
I appreciate any help.TomResearcher@University of CordobaSpain 		 	   		  
	[[alternative HTML version deleted]]

It's not clear to me what problem you're having.

   tan(data$slope)

should work.  As should

   log(data$uparea/data$slope)

I suggest that you provide a small subset of example data along with an 
example of any code you've tried, and the output that you'd like.

Jean

Tom Vanwalleghem wrote on 08/25/2011 05:54:01 AM:
> 
> Dear R helpers,
> I'm new to R and struggling with applying functions to a spatial 
> grid data frame, called data for example.data has a variable named 
> "slope" and "uparea"
> Basically, I need to calculate the tan(data$slope)Next, I need to 
> divide data$uparea by data$slope and take the log() of that all
> In the basic examples I found how to make simple multiplications 
> with a scalar likedata[["slope"]] = data[["slope"]]/2 #
assigns new
attribute
> I come from a background in GIS and fortran, so used to dealing with
> ordinary matrices, I'll admit I'm having trouble with understanding
> the format of this spatial grid data frame structureI've been trying
> different methods to index the data frame, or working with the 
> function "lapply" but so far I can't seem to get my head
wrapped around
it.
> I appreciate any help.TomResearcher@University of CordobaSpain  
>    [[alternative HTML version deleted]]
> 
	[[alternative HTML version deleted]]

On 08/25/2011 10:54 AM, Tom Vanwalleghem wrote:
> Dear R helpers,
> I'm new to R and struggling with applying functions to a spatial grid
data frame, called data for example.data has a variable named "slope"
and "uparea"
> Basically, I need to calculate the tan(data$slope)Next, I need to divide
data$uparea by data$slope and take the log() of that all
> In the basic examples I found how to make simple multiplications with a
scalar likedata[["slope"]] = data[["slope"]]/2 # assigns new
attribute
> I come from a background in GIS and fortran, so used to dealing with
ordinary matrices, I'll admit I'm having trouble with understanding the
format of this spatial grid data frame structureI've been trying different
methods to index the data frame, or working with the function "lapply"
but so far I can't seem to get my head wrapped around it.
> I appreciate any help.TomResearcher at University of CordobaSpain
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
I would most surely take a look at the raster package, this might also
be more intuitive for you. In addition, there is a special mailing list
for spatial tasks, r-sig-geo. These kinds of questions are more suitable
for that mailing list.

cheers,
Paul

-- 
Paul Hiemstra, Ph.D.
Global Climate Division
Royal Netherlands Meteorological Institute (KNMI)
Wilhelminalaan 10 | 3732 GK | De Bilt | Kamer B 3.39
P.O. Box 201 | 3730 AE | De Bilt
tel: +31 30 2206 494

http://intamap.geo.uu.nl/~paul
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