combn - Performing a function on all possible combinations of a subset of DF columns in R -

i'd calculate distance between row-wise pairs of lat/long coordinates. done variety of functions earth.dist. stuck i'd part of nightly data quality check process number of pairs changes. each row unique subject/person. days few subjects have 4 sets of coordinates, days largest might three. there elegant way perform calculate using, e.g., of possible combinations formed by:

combn(geototal, 2]) 

, geototal number of coordinate sets on given day, e.g. x = 4 set:

latitude.1, longitude.1, latitude.2, longitude.2, latitude.3, longitude.3 latitude.4, longitude.4.

my current loop looks of course misses many possible combinations, esp. x gets larger 4.

x = 1; y = 2  while(x <= geototal)  {   if (y > geototal) break;   eval(parse(text = sprintf("df$distance%d_%d = earth.dist(longitude.%d,latitude.%d,longitude.%d,latitude.%d)", x, y, x, x, y, y)));   x <- x + 1;    y <- y + 1; } 

thank thoughts on this!

try this

# using built in dataset library(fossil) data(fdata.lats) df = fdata.lats@coords  # function calculate pairwise distance foo = function(df) {   # find number of pairs   n = nrow(df)   # find combination   l = t(combn(n, 2))   # loop on combination , calculate distance, store output in vector   t = apply(l, 1, function(x) {earth.dist(df[x,])})   # return list of pairs , distance, modify here if want print instead   cbind(l, t) }  # test run foo(df)                      t  [1,]  1  2  893.4992  [2,]  1  3  776.3101  [3,]  1  4 1101.1145  [4,]  1  5 1477.4800  [5,]  1  6  444.9052  [6,]  1  7  456.5888  [7,]  1  8 1559.4614  [8,]  1  9 1435.2985  [9,]  1 10 1481.0119 [10,]  1 11 1152.0352 [11,]  1 12  870.4960 [12,]  2  3  867.2648 [13,]  2  4  777.6345 [14,]  2  5  860.9163 ...