diff --git a/Project.toml b/Project.toml
index f620db1..b5c159f 100644
--- a/Project.toml
+++ b/Project.toml
@@ -5,6 +5,7 @@ version = "0.5.2"
 [deps]
 Distances = "b4f34e82-e78d-54a5-968a-f98e89d6e8f7"
 
+
 [compat]
 julia = "1"
 Distances = "0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8"
diff --git a/src/StringDistances.jl b/src/StringDistances.jl
index 882f9b4..7939d30 100755
--- a/src/StringDistances.jl
+++ b/src/StringDistances.jl
@@ -17,8 +17,6 @@ include("find.jl")
 ##
 ##############################################################################
 
-evaluate(::QGramDistance, ::Missing, ::AbstractString) = missing
-evaluate(::QGramDistance, ::AbstractString, ::Missing) = missing
 
 evaluate(::RatcliffObershelp, ::Missing, ::AbstractString) = missing
 evaluate(::RatcliffObershelp, ::AbstractString, ::Missing) = missing
diff --git a/src/edit.jl b/src/edit.jl
index eea55c2..116af1e 100755
--- a/src/edit.jl
+++ b/src/edit.jl
@@ -239,7 +239,7 @@ end
 
 function matching_blocks!(x::Set{Tuple{Int, Int, Int}}, s1::AbstractString, s2::AbstractString, 
     len1::Integer, len2::Integer, start1::Integer, start2::Integer)
-    a = longest_common_substring(s1, s2, len1 , len2)
+    a = longest_common_pattern(s1, s2, len1 , len2)
     # exit if there is no common substring
     a[3] == 0 && return x
     # add the info of the common to the existing set
@@ -256,11 +256,9 @@ function matching_blocks!(x::Set{Tuple{Int, Int, Int}}, s1::AbstractString, s2::
     return x
 end
 
-# Return start of commn substring in s1, start of common substring in s2, and length of substring
-# Indexes refer to character number, not index
-function longest_common_substring(s1::AbstractString, s2::AbstractString, len1::Integer, len2::Integer)
+function longest_common_pattern(s1::AbstractString, s2::AbstractString, len1::Integer, len2::Integer)
     if len1 > len2
-        start2, start1, len = longest_common_substring(s2, s1, len2, len1)
+        start2, start1, len = longest_common_pattern(s2, s1, len2, len1)
     else
         start1, start2, len = 0, 0, 0
         p = zeros(Int, len2)
diff --git a/src/qgram.jl b/src/qgram.jl
index 010163c..7c1e659 100755
--- a/src/qgram.jl
+++ b/src/qgram.jl
@@ -1,10 +1,11 @@
-
-struct QGramIterator{S <: AbstractString}
-	s::S   # string
+struct QGramIterator{S}
+	s::S   # String or Iterator
 	q::Int # Length of Qgram
 end
+Base.length(qgram::QGramIterator) = max(length(qgram.s) - qgram.q + 1, 0)
 
-function Base.iterate(qgram::QGramIterator, 
+# q-grams of AbstractString
+function Base.iterate(qgram::QGramIterator{<: AbstractString}, 
 	state = (1, nextind(qgram.s, 0, qgram.q)))
 	istart, iend = state
 	iend > ncodeunits(qgram.s) && return nothing
@@ -12,15 +13,22 @@ function Base.iterate(qgram::QGramIterator,
 	nextstate = nextind(qgram.s, istart), nextind(qgram.s, iend)
 	element, nextstate
 end
-Base.length(qgram::QGramIterator) = max(length(qgram.s) - qgram.q + 1, 0)
 Base.eltype(qgram::QGramIterator{SubString{S}}) where {S} = SubString{S}
-Base.eltype(qgram::QGramIterator{S}) where {S} = SubString{S}
+Base.eltype(qgram::QGramIterator{S}) where {S <: AbstractString} = SubString{S}
+
+
+
+function Base.iterate(qgram::QGramIterator{<: AbstractVector}, state = firstindex(qgram.s))
+	state + qgram.q - 1 > lastindex(qgram.s) && return nothing
+	view(qgram.s, state:(state + qgram.q - 1)), state + 1
+end
+Base.eltype(qgram::QGramIterator{<: AbstractVector}) = typeof(first(qgram))
 
 """
 Return an iterator on the q-gram of a string
 
 ### Arguments
-* `s::AbstractString`
+* `s` iterator
 * `q::Integer`: length of q-gram
 
 ## Examples
@@ -30,7 +38,9 @@ for x in qgrams("hello", 2)
 end
 ```
 """
-qgrams(s::AbstractString, q::Integer) = QGramIterator{typeof(s)}(s, q)
+qgrams(s::AbstractString, q::Integer) = QGramIterator(s, q)
+qgrams(s::AbstractVector, q::Integer) = QGramIterator(s, q)
+qgrams(s, q::Integer) = QGramIterator(collect(s), q)
 
 
 
@@ -84,7 +94,8 @@ struct QGram <: QGramDistance
 	q::Int
 end
 
-function evaluate(dist::QGram, s1::AbstractString, s2::AbstractString)
+function evaluate(dist::QGram, s1, s2)
+	(ismissing(s1) | ismissing(s2)) && return missing
 	itr = values(count_map(qgrams(s1, dist.q), qgrams(s2, dist.q)))
 	n = 0
 	itr = 
@@ -110,7 +121,8 @@ struct Cosine <: QGramDistance
 	q::Int
 end
 
-function evaluate(dist::Cosine, s1::AbstractString, s2::AbstractString)
+function evaluate(dist::Cosine, s1, s2)
+	(ismissing(s1) | ismissing(s2)) && return missing
 	itr = values(count_map(qgrams(s1, dist.q), qgrams(s2, dist.q)))
 	norm1, norm2, prodnorm = 0, 0, 0
 	for (n1, n2) in itr
@@ -136,7 +148,8 @@ struct Jaccard <: QGramDistance
 	q::Int
 end
 
-function evaluate(dist::Jaccard, s1::AbstractString, s2::AbstractString)
+function evaluate(dist::Jaccard, s1, s2)
+	(ismissing(s1) | ismissing(s2)) && return missing
 	itr = values(count_map(qgrams(s1, dist.q), qgrams(s2, dist.q)))
 	ndistinct1, ndistinct2, nintersect = 0, 0, 0
 	for (n1, n2) in itr
@@ -162,7 +175,8 @@ struct SorensenDice <: QGramDistance
 	q::Int
 end
 
-function evaluate(dist::SorensenDice, s1::AbstractString, s2::AbstractString)
+function evaluate(dist::SorensenDice, s1, s2)
+	(ismissing(s1) | ismissing(s2)) && return missing
 	itr = values(count_map(qgrams(s1, dist.q), qgrams(s2, dist.q)))
 	ndistinct1, ndistinct2, nintersect = 0, 0, 0
 	for (n1, n2) in itr
@@ -188,7 +202,8 @@ struct Overlap <: QGramDistance
 	q::Int
 end
 
-function evaluate(dist::Overlap, s1::AbstractString, s2::AbstractString)
+function evaluate(dist::Overlap, s1, s2)
+	(ismissing(s1) | ismissing(s2)) && return missing
 	itr = values(count_map(qgrams(s1, dist.q), qgrams(s2, dist.q)))
 	ndistinct1, ndistinct2, nintersect = 0, 0, 0
 	for (n1, n2) in itr
diff --git a/test/distances.jl b/test/distances.jl
index 34b1dbc..329d6da 100644
--- a/test/distances.jl
+++ b/test/distances.jl
@@ -143,10 +143,12 @@ using StringDistances, Test
 end
 
 
-
+# allow any iterator 
 evaluate(Jaro(), [1,2,3], [1,2,10])
 evaluate(Levenshtein(), [1,2,3], [1,2,10])
 evaluate(DamerauLevenshtein(), [1,2,3], [1,2,10])
+evaluate(QGram(2), [1,2,3], [1,2,10])
+evaluate(Overlap(2), [1,2,3], [1,2,10])
 
 
 #= R test