Task: Stem-and-leaf plot
Java: import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

public class StemAndLeaf {
	private static int[] data = { 12, 127, 28, 42, 39, 113, 42, 18, 44, 118,
			44, 37, 113, 124, 37, 48, 127, 36, 29, 31, 125, 139, 131, 115, 105,
			132, 104, 123, 35, 113, 122, 42, 117, 119, 58, 109, 23, 105, 63,
			27, 44, 105, 99, 41, 128, 121, 116, 125, 32, 61, 37, 127, 29, 113,
			121, 58, 114, 126, 53, 114, 96, 25, 109, 7, 31, 141, 46, 13, 27,
			43, 117, 116, 27, 7, 68, 40, 31, 115, 124, 42, 128, 52, 71, 118,
			117, 38, 27, 106, 33, 117, 116, 111, 40, 119, 47, 105, 57, 122,
			109, 124, 115, 43, 120, 43, 27, 27, 18, 28, 48, 125, 107, 114, 34,
			133, 45, 120, 30, 127, 31, 116, 146 };
	
	public static Map<Integer, List<Integer>> createPlot(int... data){
		Map<Integer, List<Integer>> plot = new TreeMap<Integer, List<Integer>>();
		int highestStem = -1; 
		for(int datum:data){
			int leaf = datum % 10;
			int stem = datum / 10; 
			if(stem > highestStem){
				highestStem = stem;
			}
			if(plot.containsKey(stem)){
				plot.get(stem).add(leaf);
			}else{
				LinkedList<Integer> list = new LinkedList<Integer>();
				list.add(leaf);
				plot.put(stem, list);
			}
		}
		if(plot.keySet().size() < highestStem + 1  ){
			for(int i = 0; i <= highestStem; i++){
				if(!plot.containsKey(i)){
					LinkedList<Integer> list = new LinkedList<Integer>();
					plot.put(i, list);
				}
			}
		}
		return plot;
	}
	
	public static void printPlot(Map<Integer, List<Integer>> plot){
		for(Map.Entry<Integer, List<Integer>> line : plot.entrySet()){
			Collections.sort(line.getValue());
			System.out.println(line.getKey() + " | " + line.getValue());
		}
	}
	
	public static void main(String[] args){
		Map<Integer, List<Integer>> plot = createPlot(data);
		printPlot(plot);
	}
}

Python: from collections import namedtuple
from pprint import pprint as pp
from math import floor

Stem = namedtuple('Stem', 'data, leafdigits')

data0 = Stem((12, 127, 28, 42, 39, 113, 42, 18, 44, 118, 44, 37, 113, 124, 37,
              48, 127, 36, 29, 31, 125, 139, 131, 115, 105, 132, 104, 123, 35,
              113, 122, 42, 117, 119, 58, 109, 23, 105, 63, 27, 44, 105, 99,
              41, 128, 121, 116, 125, 32, 61, 37, 127, 29, 113, 121, 58, 114,
              126, 53, 114, 96, 25, 109, 7, 31, 141, 46, 13, 27, 43, 117, 116,
              27, 7, 68, 40, 31, 115, 124, 42, 128, 52, 71, 118, 117, 38, 27,
              106, 33, 117, 116, 111, 40, 119, 47, 105, 57, 122, 109, 124, 115,
              43, 120, 43, 27, 27, 18, 28, 48, 125, 107, 114, 34, 133, 45, 120,
              30, 127, 31, 116, 146),
             1.0)

def stemplot(stem):
    d = []
    interval = int(10**int(stem.leafdigits))
    for data in sorted(stem.data):
        data = int(floor(data))
        stm, lf = divmod(data,interval)
        d.append( (int(stm), int(lf)) )
    stems, leafs = list(zip(*d))
    stemwidth = max(len(str(x)) for x in stems)
    leafwidth = max(len(str(x)) for x in leafs)
    laststem, out = min(stems) - 1, []
    for s,l in d:
        while laststem < s:
            laststem += 1
            out.append('\n%*i |' % ( stemwidth, laststem))
        out.append(' %0*i' % (leafwidth, l))
    out.append('\n\nKey:\n Stem multiplier: %i\n X | Y  =>  %i*X+Y\n'
               % (interval, interval))
    return ''.join(out)

if __name__ == '__main__':
    print( stemplot(data0) )