X-Git-Url: http://nitlanguage.org

diff --git a/lib/counter.nit b/lib/counter.nit
index 6d5729d..e539bc5 100644
--- a/lib/counter.nit
+++ b/lib/counter.nit
@@ -53,14 +53,14 @@ class Counter[E]
 	redef fun iterator do return map.iterator
 
 	# The number of counted occurrences of `e`
-	redef fun [](e: E): Int
+	redef fun [](e)
 	do
 		var map = self.map
 		if map.has_key(e) then return map[e]
 		return 0
 	end
 
-	redef fun []=(e: E, value: Int)
+	redef fun []=(e, value)
 	do
 		sum -= self[e]
 		self.map[e] = value
@@ -80,6 +80,12 @@ class Counter[E]
 		map.clear
 	end
 
+	redef fun add_all(other) do
+		for k, v in other do
+			self[k] += v
+		end
+	end
+
 	# Count one more occurrence of `e`
 	fun inc(e: E)
 	do
@@ -133,6 +139,7 @@ class Counter[E]
 	# @toimplement by default just call `to_s` on the element
 	protected fun element_to_s(e: E): String
 	do
+		if e == null then return "null"
 		return e.to_s
 	end
 
@@ -254,6 +261,81 @@ class Counter[E]
 		end
 		return (sum / map.length.to_f).sqrt
 	end
+
+	# The information entropy (Shannon entropy) of the elements in the counter (in bits).
+	fun entropy: Float
+	do
+		var res = 0.0
+		var sum = self.sum.to_f
+		for k, v in self do
+			var f = v.to_f / sum
+			res = res - f * f.log_base(2.0)
+		end
+		return res
+	end
+
+	# Prints the content of the counter along with statistics
+	#
+	# Content is printed in order (if available) from lowest to highest on the keys.
+	# Else, it is printed as-is
+	fun print_content do
+		var a = keys.to_a
+		if a isa Array[Comparable] then default_comparator.sort(a)
+		var subtotal = 0
+		for i in a do
+			subtotal += self[i]
+			printn("* ", i or else "null", " = ", self[i], " => occurences ", self[i].to_f / sum.to_f * 100.0, "%, cumulative ", subtotal.to_f / sum.to_f * 100.0, "% \n")
+		end
+	end
+
+	# Packs elements into separate arrays based on their occurences
+	#
+	# ~~~nit
+	#	var x = "aaaabbbeeecccddhhgjt"
+	#	var c = new Counter[Char]
+	#	for i in x do c.inc i
+	#	var ret = c.pack
+	#	assert ret.join(", ") == """[t,g,j], [d,h], [c,b,e], [a]"""
+	# ~~~
+	fun pack: Array[Array[E]] do
+		var ret = new Array[Array[E]]
+		var base = self.sort
+		if base.is_empty then return ret
+		var curr = new Array[E]
+		curr.push base.first
+		var curr_score = self[base.first]
+		base.shift
+		for i in base do
+			if self[i] == curr_score then
+				curr.push i
+				continue
+			end
+			curr_score = self[i]
+			ret.push curr
+			curr = new Array[E]
+			curr.push i
+		end
+		if not curr.is_empty then ret.push curr
+		return ret
+	end
+end
+
+redef class Collection[E]
+	# Create and fill up a counter with the elements of `self.
+	#
+	# ~~~
+	# var cpt = "abaa".chars.to_counter
+	# assert cpt['a'] == 3
+	# assert cpt['b'] == 1
+	# assert cpt.length == 2
+	# assert cpt.sum == 4
+	# ~~~
+	fun to_counter: Counter[E]
+	do
+		var res = new Counter[E]
+		res.inc_all(self)
+		return res
+	end
 end
 
 private class CounterComparator[E]