kohonen-net/utils.js

simple implementation of a self organizing map

var num = require('numeric');


function random_tensor(dimensions){

  return dimension(0);

  function dimension(index){
    let ret = [];
    for(var i=0; i<dimensions[index]; i++){
      if (index+1 != dimensions.length){
        ret.push(dimension(index+1));
      } else {
        ret.push(Math.random());
      }
    }
    return ret;
  }

}


// generates a mxm matrix containing the distance from each node in a tensor of
// arebtrary shape
function neighbourMatrix(shape, distanceFn, wrapAround){
  if (typeof(distanceFn) == 'undefined') { distanceFn = euclideanDistance; }
  if (typeof(wrapAround) == 'undefined') { wrapAround = false; }
  let totalValues = shape.reduce((p, v) => p*v, 1);
  ret = [];
  for (let m=0; m<totalValues;m++){
    row = [];
    nodeIndex = unravelIndex(m, shape);
    for (let n=0; n<totalValues;n++){
      distance = num.abs(num.sub(unravelIndex(n, shape), nodeIndex));
      if (wrapAround) {
        for(let i=0;i<shape.length;i++){
          if (distance[i] > shape[i]/2) {
            distance[i] = shape[i] - distance[i];
          }
        }
      }
      row.push(distanceFn(distance));
    }
    ret.push(row);
  }
  return ret;
}

function manhattanDistance(distance){
  return num.sum(distance);
}

function chessBoardDistance(distance){
  return num.max(distance);
}

function euclideanSquaredDistance(distance){
  return num.sum(num.pow(distance, 2));
}

function euclideanDistance(distance){
  return num.sqrt(euclideanSquaredDistance(distance));
}

// returns multidimentional index from flattend index
function unravelIndex(index, shape){
  let mdIndex = [];
  let rest = index;
  for (let i=0;i<shape.length-1;i++){
    mdIndex.push(Math.floor(rest/shape[i]));
    rest %= shape[i];
  }
  mdIndex.push(rest);
  return mdIndex;
}

// returns index of smallest value
function argMin(array){
  return array.reduce((min, val, i, arr)=> val<arr[min]?i:min, 0);
}


module.exports.random_tensor = random_tensor;
module.exports.unravelIndex = unravelIndex;
module.exports.neighbourMatrix = neighbourMatrix;
module.exports.argMin = argMin;

// distances
module.exports.manhattanDistance = manhattanDistance;
module.exports.chessBoardDistance = chessBoardDistance;
module.exports.euclideanSquaredDistance = euclideanSquaredDistance;
module.exports.euclideanDistance = euclideanDistance;