Hi,
This would be a lot easier to answer if you provided a small test
dataset using dput(); I have trouble working through code if I have no
idea what the input data looks like.
One thing I did spot is a problem in your indexing:
j is a scalar, so indexing j[2] won't work. Presumably you got the
brackets wrong, and want cells[j][1] and cells[j][2], but again,
without knowing what cells is, I can't say for certain.
These are the lines I'm referring to:
Row<-BasinPollutant[cells[j[1]]]
Column<-BasinPollutant[cells[j[2]]]
Sarah
On Mon, Mar 24, 2014 at 10:02 AM, Vermeulen, Lucie
<lucie.vermeu...@wur.nl> wrote:
> I am trying to write an R script to do pollution routing in world rivers, and
> need some help on selecting matrix cell coordinates and applying these to
> other matrices of the same dimension.
>
> My data: I have several matrices corresponding to hydrological parameters of
> world rivers on a half degree grid (360 rows, 720 columns). These matrices
> represent flow accumulation (how many cells flow into this cell), flow
> direction (which of the 8 surrounding cells does the load of certain cell
> flow to) and pollutant load.
>
> My idea: compute pollutant load in each grid cell from the start to the end
> of a river. I can base this on flow accumulation (low to high). However, each
> river basin can have multiple cells with the same flow accumulation value.
>
> The problem: I need to select all matrix cells of each value of flow
> accumulation (low to high), find their coordinates (row,column), and transfer
> the corresponding pollutant load to the correct adjacent cell using the flow
> direction matrix. I have tried various ways, but selecting the coordinates of
> the correct cells and applying these to another matrix I cannot get to work.
>
> I will give an example of what I have tried, using two for loops on one
> single river basin. In this example, a flow direction value of 1 means that
> the pollutant load needs to be transferred to the adjacent cell to the right
> (row is the same, column +1):
>
> BasinFlowAccumulation <-FlowAccumulation[Basin]
>
> BasinFlowAccumulationMaximum <- max(BasinFlowAccumulation)
>
> BasinFlowDirection <-FlowDirection[Basin]
>
> BasinPollutant <-Pollutant[Basin]
>
>
> b<-0
>
> for(i in 0:BasinFlowAccumulationMaximum){
>
> cells.index<-which(BasinFlowAccumulation[]==b, arr.ind=TRUE)
>
> for (j in 1:length(cells.index)){
> print(BasinFlowDirection[cells[j]])
> Row<-BasinPollutant[cells[j[1]]]
> Column<-BasinPollutant[cells[j[2]]]
> ifelse(BasinFlowDirection[cells.index[j]]==1,
> BasinPollutant[Row,(Column+1)]<- BasinPollutant [Row,(Column+1)]+
> BasinPollutant [Row,Column]
>
> }
> b<-b+1
>
> }
>
--
Sarah Goslee
http://www.functionaldiversity.org
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