1 files changed, 32 insertions, 0 deletions
diff --git a/lib/nlp_ruby/tfidf.rb b/lib/nlp_ruby/tfidf.rb
new file mode 100644
index 0000000..84d55a5
--- /dev/null
+++ b/lib/nlp_ruby/tfidf.rb
@@ -0,0 +1,32 @@
+# returns key='raw frequency' for an
+# array-like object
+def tf array, stopwords=[]
+  v = {}; v.default = 0
+  array.uniq.each { |i|
+   next if stopwords.include? i
+   v[i] = array.count(i).to_f
+  }
+  return v
+end
+
+# smoothes raw frequencies of tf() in-place
+# a is a smoothing term
+def ntf hash, a=0.4
+  max = hash.values.max.to_f
+  hash.each_pair { |k,v|
+    hash[k] = a + (1-a)*(v/max)
+  }
+end
+
+# returns idf value for each word in a vocabulary
+def idf list_of_hashes
+  vocab = list_of_hashes.values.flatten.uniq
+  n = list_of_hashes.size.to_f
+  idf = {}
+  vocab.each { |i|
+    df = list_of_hashes.values.flatten.count i
+    idf[i] = Math.log(n/df)
+  }
+  return idf
+end
+