title: Get raster cell coordinates using the 'calc' function in R
body: <p>I am trying to run a 'calc' function in R and I can't seem to find a way to obtain the coordinates of the cell that is being processed. What I'm trying to do is simple :
  Using the 'calc' function on a binary raster (0 and 1)-- If the raster value is '0', then change to 'NA'. If the raster value is '1', then apply a series of processes for which I will need to cell coordinates to be stored into variables.</p>
  
  <pre><code>processAllCells = function(cell) {
    if (cell == 0) {
      cell = NA
      return(cell) 
    }
    else {
      cellCoords = coordinates(cell) ### This is what I'm trying to do. This does not work. See the error message.
      ### Here will go further processes using the cell coordinates.
      return(cell)
    }
  }
  
  outputRaster = calc(lake, processAllCells)
  </code></pre>
  
  <p>Error message :</p>
  
  <pre><code>Error in (function (classes, fdef, mtable)  : 
    unable to find an inherited method for function ‘coordinates’ for signature ‘"integer"’
  In addition: Warning message:
  In if (cell == 0) { :
  
   Error in (function (classes, fdef, mtable)  : 
    unable to find an inherited method for function ‘coordinates’ for signature ‘"integer"’ 
  </code></pre>
  
  <p>Thanks everyone!</p>