Gist for map-reduce, assuming prior Gist here: http://www.manchicken.com/2013/hacking/gist-of-the-day-csv_into_mongo-py-2-of-2.html and CSV file here: http://manchicken.kd.io/foo.csv

map_reduce.mongo.js

db.foo.find().forEach(printjson);

db.foo.mapReduce(
  function () {
    emit (this["First Name"].toLowerCase().split('')[0], 1);
  },
  function (key,value) {
    return Array.sum(value);
  },
  {
    out : "foo_out"
  }
);

db.foo_out.find().forEach(printjson);