Here is an example of how word count is performed using lua-mapreduce.

example/task-file.lua is a sample task-file for work count which implements following functions. Each of these functions are invoked using coroutines to avoid non-blocking calls so as well as returning results one entry at a time to save the memory.

All these functions must be defines as part of table and return this table in function mapreduce()

1. taskfn: It reads the source and creates the map of the tasks. E.g For word count, it reads the all file with .lua from current directory and creates a map with key as a file name and content as a value.

	mr.taskfn = function()
		--logger:debug("Getting map task")
		local tasks = read_source()  -- read source is utility function defined to read data source
		for key, value in pairs(tasks) do
			coroutine.yield(key, value)
		end
	end

Here read_source() is a local function defined as below. NOTE: it uses luafilesystem (lfs) module to read the files

	local function read_source()
	  --local file_path = system.pathForFile( "*.lua", lfs.currentdir() )
	  local file_path = lfs.currentdir()
	  --logger:debug("Current directory path:" .. file_path)
	  local source_table = {}
	  for file in lfs.dir(file_path) do
	    if(string.find(file, ".lua") ~= nil) then
		--	logger:debug("File name:" .. file_path .. "/" .. file)
			local c = read_file(file_path .. "/" .. file)
		--	logger:debug("file:" .. file .. ", length:" .. #c)
			if( c ~= nil) then
				source_table[file]=c
			end
		end
	  end
	  return source_table
	end

2. finalfn : How to output final result. Here it prints on the console.

    mr.finalfn = function (results)
		print("Final results of the task:")
		for key, value in pairs(results) do
			print( key .. ":" .. value)
			coroutine.yield()
		end
	end

1. mapfn: Map function which processes the task (content of the file here) and splits into lines and each lines into words

-- Map function : Here it splits the content of the files into lines and each line into words
	mr.mapfn = function(key, value)
		--logger:debug("mapfn with key:" .. key .. ", value :" .. value .. "\r\n\r\n")
		local file_words = {}
		local lines = value:split("[^\r\n%s]+")
	--	logger:debug("Number of lines in " .. #lines .. " in the file " .. key)
		for k, w in  ipairs(lines) do
			if(w ~= nil) then
				local words = {}
				string.gsub(w, "(%a+)", function (word)
					table.insert(words, string.lower(word))
				end)
				--local words = w:split("[^ %s]+")
				if(words ~= nil) then
					--logger:debug("Number of words in line " .. k .. " are " .. #words)
					for j=1, #words do
						--logger:debug("mapfn:yielding " .. words[j])
						coroutine.yield(words[j], 1)
					end
				end
			end
		end
	end

2. reducefn : Reduce function which processes the number of occurrences for a word. Here it returns the size of an array.

	---Reduce function: It returns the numbe of entries for the values
	mr.reducefn = function (key, value)
		--logger:debug("reducefn: for key:" .. key ..  ", number of words  :" .. #value)
		coroutine.yield(key, #value)
	end