diff --git a/base/sparse/csparse.jl b/base/sparse/csparse.jl
index f97d8972126f2..e36183bb72946 100644
--- a/base/sparse/csparse.jl
+++ b/base/sparse/csparse.jl
@@ -300,64 +300,4 @@ function symperm{Tv,Ti}(A::SparseMatrixCSC{Tv,Ti}, pinv::Vector{Ti})
         end
     end
     (C.').' # double transpose to order the columns
-end
-
-# Based on Direct Methods for Sparse Linear Systems, T. A. Davis, SIAM, Philadelphia, Sept. 2006.
-# Section 2.7: Removing entries from a matrix
-# http://www.cise.ufl.edu/research/sparse/CSparse/
-function fkeep!{Tv,Ti}(A::SparseMatrixCSC{Tv,Ti}, f, other)
-    nzorig = nnz(A)
-    nz = 1
-    colptr = A.colptr
-    rowval = A.rowval
-    nzval = A.nzval
-    @inbounds for j = 1:A.n
-        p = colptr[j]                 # record current position
-        colptr[j] = nz                # set new position
-        while p < colptr[j+1]
-            if f(rowval[p], j, nzval[p], other)
-                nzval[nz] = nzval[p]
-                rowval[nz] = rowval[p]
-                nz += 1
-            end
-            p += 1
-        end
-    end
-    colptr[A.n + 1] = nz
-    nz -= 1
-    if nz < nzorig
-        resize!(nzval, nz)
-        resize!(rowval, nz)
-    end
-    A
-end
-
-
-immutable DropTolFun <: Func{4} end
-(::DropTolFun)(i,j,x,other) = abs(x)>other
-immutable DropZerosFun <: Func{4} end
-(::DropZerosFun)(i,j,x,other) = x!=0
-immutable TriuFun <: Func{4} end
-(::TriuFun)(i,j,x,other) = j>=i + other
-immutable TrilFun <: Func{4} end
-(::TrilFun)(i,j,x,other) = i>=j - other
-
-droptol!(A::SparseMatrixCSC, tol) = fkeep!(A, DropTolFun(), tol)
-dropzeros!(A::SparseMatrixCSC) = fkeep!(A, DropZerosFun(), nothing)
-dropzeros(A::SparseMatrixCSC) = dropzeros!(copy(A))
-
-function triu!(A::SparseMatrixCSC, k::Integer=0)
-    m,n = size(A)
-    if (k > 0 && k > n) || (k < 0 && -k > m)
-        throw(BoundsError())
-    end
-    fkeep!(A, TriuFun(), k)
-end
-
-function tril!(A::SparseMatrixCSC, k::Integer=0)
-    m,n = size(A)
-    if (k > 0 && k > n) || (k < 0 && -k > m)
-        throw(BoundsError())
-    end
-    fkeep!(A, TrilFun(), k)
-end
+end
\ No newline at end of file
diff --git a/base/sparse/sparsematrix.jl b/base/sparse/sparsematrix.jl
index 21fab807e582d..116b330dffc16 100644
--- a/base/sparse/sparsematrix.jl
+++ b/base/sparse/sparsematrix.jl
@@ -479,6 +479,93 @@ transpose{Tv,Ti}(A::SparseMatrixCSC{Tv,Ti}) = qftranspose(A, 1:A.n, Base.IdFun()
 ctranspose{Tv,Ti}(A::SparseMatrixCSC{Tv,Ti}) = qftranspose(A, 1:A.n, Base.ConjFun())
 "See `qftranspose`" ftranspose{Tv,Ti}(A::SparseMatrixCSC{Tv,Ti}, f) = qftranspose(A, 1:A.n, f)
 
+
+## fkeep! and children tril!, triu!, droptol!, dropzeros[!]
+
+"""
+    fkeep!{Tv,Ti}(A::SparseMatrixCSC{Tv,Ti}, f, other, trim::Bool = true)
+
+Keep elements of `A` for which test `f` returns `true`. `f`'s signature should be
+
+    f{Tv,Ti}(i::Ti, j::Ti, x::Tv, other::Any) -> Bool
+
+where `i` and `j` are an element's row and column indices, `x` is the element's value,
+and `other` is passed in from the call to `fkeep!`. This method makes a single sweep
+through `A`, requiring `O(A.n, nnz(A))`-time and no space beyond that passed in. If `trim`
+is `true`, this method trims `A.rowval` and `A.nzval` to length `nnz(A)` after dropping
+elements.
+
+Performance note: As of January 2016, `f` should be a functor for this method to perform
+well. This caveat may disappear when the work in `jb/functions` lands.
+"""
+function fkeep!{Tv,Ti}(A::SparseMatrixCSC{Tv,Ti}, f, other, trim::Bool = true)
+    An = A.n
+    Acolptr = A.colptr
+    Arowval = A.rowval
+    Anzval = A.nzval
+
+    # Sweep through columns, rewriting kept elements in their new positions
+    # and updating the column pointers accordingly as we go.
+    Awritepos = 1
+    oldAcolptrAj = 1
+    @inbounds for Aj in 1:An
+        for Ak in oldAcolptrAj:(Acolptr[Aj+1]-1)
+            Ai = Arowval[Ak]
+            Ax = Anzval[Ak]
+            # If this element should be kept, rewrite in new position
+            if f(Ai, Aj, Ax, other)
+                if Awritepos != Ak
+                    Arowval[Awritepos] = Ai
+                    Anzval[Awritepos] = Ax
+                end
+                Awritepos += 1
+            end
+        end
+        oldAcolptrAj = Acolptr[Aj+1]
+        Acolptr[Aj+1] = Awritepos
+    end
+
+    # Trim A's storage if necessary and desired
+    if trim
+        Annz = Acolptr[end] - 1
+        if length(Arowval) != Annz
+            resize!(Arowval, Annz)
+        end
+        if length(Anzval) != Annz
+            resize!(Anzval, Annz)
+        end
+    end
+
+    A
+end
+
+immutable TrilFunc <: Base.Func{4} end
+immutable TriuFunc <: Base.Func{4} end
+call{Tv,Ti}(::TrilFunc, i::Ti, j::Ti, x::Tv, k::Integer) = i + k >= j
+call{Tv,Ti}(::TriuFunc, i::Ti, j::Ti, x::Tv, k::Integer) = j >= i + k
+function tril!(A::SparseMatrixCSC, k::Integer = 0, trim::Bool = true)
+    if k > A.n-1 || k < 1-A.m
+        throw(ArgumentError("requested diagonal, $k, out of bounds in matrix of size ($(A.m),$(A.n))"))
+    end
+    fkeep!(A, TrilFunc(), k, trim)
+end
+function triu!(A::SparseMatrixCSC, k::Integer = 0, trim::Bool = true)
+    if k > A.n-1 || k < 1-A.m
+        throw(ArgumentError("requested diagonal, $k, out of bounds in matrix of size ($(A.m),$(A.n))"))
+    end
+    fkeep!(A, TriuFunc(), k, trim)
+end
+
+immutable DroptolFunc <: Base.Func{4} end
+call{Tv,Ti}(::DroptolFunc, i::Ti, j::Ti, x::Tv, tol::Real) = abs(x) > tol
+droptol!(A::SparseMatrixCSC, tol, trim::Bool = true) = fkeep!(A, DroptolFunc(), tol, trim)
+
+immutable DropzerosFunc <: Base.Func{4} end
+call{Tv,Ti}(::DropzerosFunc, i::Ti, j::Ti, x::Tv, other) = x != 0
+dropzeros!(A::SparseMatrixCSC, trim::Bool = true) = fkeep!(A, DropzerosFunc(), Void, trim)
+dropzeros(A::SparseMatrixCSC, trim::Bool = true) = dropzeros!(copy(A), trim)
+
+
 ## Find methods
 
 function find(S::SparseMatrixCSC)
diff --git a/test/sparsedir/sparse.jl b/test/sparsedir/sparse.jl
index c958380a4282d..61daeccb638df 100644
--- a/test/sparsedir/sparse.jl
+++ b/test/sparsedir/sparse.jl
@@ -978,6 +978,12 @@ perm = randperm(10)
 
 # droptol
 @test Base.droptol!(A,0.01).colptr == [1,1,1,2,2,3,4,6,6,7,9]
+@test isequal(Base.droptol!(sparse([1], [1], [1]), 1), SparseMatrixCSC(1,1,Int[1,1],Int[],Int[]))
+
+# dropzeros
+A = sparse([1 2 3; 4 5 6; 7 8 9])
+A.nzval[2] = A.nzval[6] = A.nzval[7] = 0
+@test Base.dropzeros!(A).colptr == [1, 3, 5, 7]
 
 #trace
 @test_throws DimensionMismatch trace(sparse(ones(5,6)))
@@ -1000,6 +1006,13 @@ AF = full(A)
 @test_throws BoundsError tril(A,-6)
 @test_throws BoundsError triu(A,6)
 @test_throws BoundsError triu(A,-6)
+@test_throws ArgumentError tril!(sparse([1,2,3], [1,2,3], [1,2,3], 3, 4), 4)
+@test_throws ArgumentError tril!(sparse([1,2,3], [1,2,3], [1,2,3], 3, 4), -3)
+@test_throws ArgumentError triu!(sparse([1,2,3], [1,2,3], [1,2,3], 3, 4), 4)
+@test_throws ArgumentError triu!(sparse([1,2,3], [1,2,3], [1,2,3], 3, 4), -3)
+
+# fkeep trim option
+@test isequal(length(tril!(sparse([1,2,3], [1,2,3], [1,2,3], 3, 4), -1).rowval), 0)
 
 # test norm