calcSummary function

Apply Functions to Polygons in a PolySet

Apply functions to polygons in a PolySet .

calcSummary (polys, rollup = 3, FUN, ...)

Arguments

• polys: PolySet to use.
• rollup: level of detail in the results; 1 = PIDs only, by removing the SID column, and then passing each PID into FUN, 2 = outer contours only, by making hole SIDs equal to their parent's SID, and then passing each (PID, SID) into FUN, and 3 = no roll-up.
• FUN: the function to apply; it must accept a vector and return a vector or scalar.
• ...: optional arguments for FUN.

Details

If rollup equals 1, the results contain an entry for each unique PID only. When it equals 2, they contain entries for outer contours only. Finally, setting it to 3

prevents roll-up, and they contain an entry for each unique (PID, SID).

Returns

PolyData with columns PID, SID (may be missing), X, and Y. If FUN returns a vector of length greater than 1 (say n), names the columns X1, X2, ..., Xn and Y1, Y2, ..., Yn.

Author(s)

Nicholas M. Boers, Staff Software Engineer

Jobber, Edmonton AB

Last modified Rd: 2013-04-10

See Also

calcArea, calcCentroid, calcConvexHull, calcLength, calcMidRange, combineEvents, findPolys, locateEvents, locatePolys, makeGrid, makeProps.

Examples

local(envir=.PBSmapEnv,expr={
  #--- load the data (if using R)
  if (!is.null(version$language) && (version$language=="R"))
    data(nepacLL,envir=.PBSmapEnv)
  #--- calculate and print the centroids for several polygons
  print(calcSummary(nepacLL[is.element(nepacLL$PID,c(33,39,47)),],
    rollup=3, FUN=mean))
})