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-- io module required for reading from stdin
require 'io'
function get_frequencies(iterator)
-- hashtable where we keep the frequencies in
local freqs = {}
-- define metatable that returns 0 instead of nil when its associated table
-- is accessed with a non-existing key
mt = { __index = function(t,word) return 0 end }
-- assign the metatable to our frequency table, the freqs table will now
-- return 0 instead of nil if a non-existing element is accessed
setmetatable(freqs, mt)
-- get the freqencies
for line in iterator() do
-- lowercase the line, then return match iterator for only "lower case word
-- characters" and iterate
for word in string.gmatch(string.lower(line), "%l+") do
-- thanks to our metatable, an access to non-existing freqs[word] entry
-- just returns 0, so the following just works(TM)
freqs[word] = freqs[word] + 1
return freqs
function mk_tuple_sequence(frequencies)
-- get a table to become a sequence of tuples
-- table layout: integers as indicies/keys, {word,frequency}-tuples as values
local result = {}
-- iterate over key/value pairs in the freqs table
for word,freq in pairs(frequencies) do
-- will insert {word,frequency} as value for next available integer index/key
-- i.e., inserting {"spam",5} into table {1={"foo",6}, 2={"bar",2}} will result in
-- {1={"foo",6}, 2={"bar",2}, 3={"spam",5}}
table.insert(result, {word,freq})
return result
-- is within the scope of an easy anonymous function but making this explicit anyway
function tuple_comparator(tuple_a, tuple_b)
return tuple_a[2] > tuple_b[2]
function order_tuple_sequence(sequence, comparator)
-- unfortunately table.sort sorts in-place
table.sort(sequence, comparator)
return sequence
function print_first_n(sequence, n)
if n ~= 0 then
-- doing head recursion here, works as expected
print_first_n(sequence, n-1)
print(string.format("%s: %i", sequence[n][1], sequence[n][2]))
-- io.lines() without argument just reads from stdin, although we pass this as a function here
print_first_n(order_tuple_sequence(mk_tuple_sequence(get_frequencies(io.lines)), tuple_comparator), 10)