Generate combinations of values which sum to one, sorted in descending order

Question

Do you know a more efficient way to generate a matrix holding all unique combinations of \"weights\" (let weights be w and 0 <= w <= 1, and values of w are separated b

Answer 1

General purpose function with standard packages:

# Generate weights matrix with noWeights columns and noRows rows.
# Each row of this matrix contains sorted decremental weights summing up to 1.0.
generateWeights = function(noWeights,
                           noRows,
                           distribution = runif,
                           rounding = function(x){ round(x, 1) })
{
  generator = function()
  {
    x = distribution (noWeights);
    x = x/sum(x);
    sort(rounding(x), decreasing = T)
  } 
  t(replicate(noRows, generator()))
}

# example of use
generateWeights(3, 10)