# user>rmr>Comparison of high level languages for mapreduce k means

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This is just a case study based on k-means. The first is an implementation from the folks at Hortonworks, in python, pig latin and java. Below is an implementation in just R. The algorithms are not identical.

## Pig

```#!/usr/bin/python
import sys
from math import fabs
from org.apache.pig.scripting import Pig

filename = "student.txt"
k = 4
tolerance = 0.01

MAX_SCORE = 4
MIN_SCORE = 0
MAX_ITERATION = 100

# initial centroid, equally divide the space
initial_centroids = ""
last_centroids = [None] * k
for i in range(k):
last_centroids[i] = MIN_SCORE + float(i)/k*(MAX_SCORE-MIN_SCORE)
initial_centroids = initial_centroids + str(last_centroids[i])
if i!=k-1:
initial_centroids = initial_centroids + ":"

P = Pig.compile("""register udf.jar
DEFINE find_centroid FindCentroid('\$centroids');
raw = load 'student.txt' as (name:chararray, age:int, gpa:double);
centroided = foreach raw generate gpa, find_centroid(gpa) as centroid;
grouped = group centroided by centroid;
result = foreach grouped generate group, AVG(centroided.gpa);
store result into 'output';
""")

converged = False
iter_num = 0
while iter_num<MAX_ITERATION:
Q = P.bind({'centroids':initial_centroids})
results = Q.runSingle()
if results.isSuccessful() == "FAILED":
raise "Pig job failed"
iter = results.result("result").iterator()
centroids = [None] * k
distance_move = 0
# get new centroid of this iteration, caculate the moving distance with last iteration
for i in range(k):
tuple = iter.next()
centroids[i] = float(str(tuple.get(1)))
distance_move = distance_move + fabs(last_centroids[i]-centroids[i])
distance_move = distance_move / k;
Pig.fs("rmr output")
print("iteration " + str(iter_num))
print("average distance moved: " + str(distance_move))
if distance_move<tolerance:
sys.stdout.write("k-means converged at centroids: [")
sys.stdout.write(",".join(str(v) for v in centroids))
sys.stdout.write("]\n")
converged = True
break
last_centroids = centroids[:]
initial_centroids = ""
for i in range(k):
initial_centroids = initial_centroids + str(last_centroids[i])
if i!=k-1:
initial_centroids = initial_centroids + ":"
iter_num += 1

if not converged:
print("not converge after " + str(iter_num) + " iterations")
sys.stdout.write("last centroids: [")
sys.stdout.write(",".join(str(v) for v in last_centroids))
sys.stdout.write("]\n")```
```import java.io.IOException;

import org.apache.pig.EvalFunc;
import org.apache.pig.data.Tuple;

public class FindCentroid extends EvalFunc<Double> {
double[] centroids;
public FindCentroid(String initialCentroid) {
String[] centroidStrings = initialCentroid.split(":");
centroids = new double[centroidStrings.length];
for (int i=0;i<centroidStrings.length;i++)
centroids[i] = Double.parseDouble(centroidStrings[i]);
}
@Override
public Double exec(Tuple input) throws IOException {
double min_distance = Double.MAX_VALUE;
double closest_centroid = 0;
for (double centroid : centroids) {
double distance = Math.abs(centroid - (Double)input.get(0));
if (distance < min_distance) {
min_distance = distance;
closest_centroid = centroid;
}
}
return closest_centroid;
}

}```

## R

And this is from folks at Revolution, in just R

```kmeans =
function(points, ncenters, iterations = 10, distfun = NULL) {
if(is.null(distfun))
distfun =
function(a,b) norm(as.matrix(a-b), type = 'F')
newCenters =
kmeans.iter(
points,
distfun,
ncenters = ncenters)
for(i in 1:iterations) {
newCenters = kmeans.iter(points, distfun, centers = newCenters)}
newCenters}

kmeans.iter =
function(points, distfun, ncenters = dim(centers)[1], centers = NULL) {
from.dfs(mapreduce(input = points,
map =
if (is.null(centers)) {
function(k,v) keyval(sample(1:ncenters,1),v)}
else {
function(k,v) {
distances = apply(centers, 1, function(c) distfun(c,v))
keyval(centers[which.min(distances),], v)}},
reduce = function(k,vv) keyval(NULL, apply(do.call(rbind, vv), 2, mean))),
to.data.frame = T)}```