Flesh out similar methods operating on SparseMatrixCSCs and make …

…them more consistent both among themselves and with other `similar` methods in Base.

base/sparse/sparsematrix.jl

@@ -249,9 +249,30 @@ function copy!(A::SparseMatrixCSC, B::SparseMatrixCSC)
     return A
 end
 
-similar(S::SparseMatrixCSC, Tv::Type=eltype(S)) = SparseMatrixCSC(S.m, S.n, copy(S.colptr), copy(S.rowval), Array{Tv}(length(S.nzval)))
-similar{Tv,Ti,TvNew,TiNew}(S::SparseMatrixCSC{Tv,Ti}, ::Type{TvNew}, ::Type{TiNew}) = SparseMatrixCSC(S.m, S.n, convert(Array{TiNew},S.colptr), convert(Array{TiNew}, S.rowval), Array{TvNew}(length(S.nzval)))
-@inline similar{Tv}(S::SparseMatrixCSC, ::Type{Tv}, d::Dims) = spzeros(Tv, d...)
+# similar with dims specifications only
+similar{Tv,Ti}(S::SparseMatrixCSC{Tv,Ti}, dims::Dims) = similar(S, Tv, Ti, dims...)
+similar{Tv,Ti}(S::SparseMatrixCSC{Tv,Ti}, m::Integer) = similar(S, Tv, Ti, m)
+similar{Tv,Ti}(S::SparseMatrixCSC{Tv,Ti}, m::Integer, n::Integer) = similar(S, Tv, Ti, m, n)
+# similar with entry type and dims specifications
+similar{Tv,Ti}(S::SparseMatrixCSC{Tv,Ti}, TvNew::Type, dims::Dims) = similar(S, TvNew, Ti, dims...)
+similar{Tv,Ti}(S::SparseMatrixCSC{Tv,Ti}, TvNew::Type, m::Integer) = similar(S, TvNew, Ti, m)
+similar{Tv,Ti}(S::SparseMatrixCSC{Tv,Ti}, TvNew::Type, m::Integer, n::Integer) = similar(S, TvNew, Ti, m, n)
+# similar with entry type, index type, and dims specifications
+similar(S::SparseMatrixCSC, TvNew::Type, TiNew::Type, dims::Dims) = similar(S, TvNew, TiNew, dims...)
+similar(S::SparseMatrixCSC, TvNew::Type, TiNew::Type, m::Integer) = SparseVector(m, similar(S.rowval, TiNew, 0), similar(S.nzval, TvNew, 0))
+similar(S::SparseMatrixCSC, TvNew::Type, TiNew::Type, m::Integer, n::Integer) = _preservestorage_similar(S, TvNew, TiNew, m, n)
+# parent method for similar that only preserves storage (for when new and old dims differ)
+function _preservestorage_similar(S::SparseMatrixCSC, TvNew::Type, TiNew::Type, m::Integer, n::Integer)
+    return SparseMatrixCSC(m, n, ones(TiNew, n+1), similar(S.rowval, TiNew), similar(S.nzval, TvNew))
+end
+# similar without specifications or with type specifications only
+similar{Tv,Ti}(S::SparseMatrixCSC{Tv,Ti}, TvNew::Type = Tv, TiNew::Type = Ti) = _preservenzstruc_similar(S, TvNew, TiNew)
+# parent method for similar that preserves nonzero structure (for when new and old dims match)
+function _preservenzstruc_similar(S::SparseMatrixCSC, TvNew::Type, TiNew::Type)
+    newcolptr = copy!(similar(S.colptr, TiNew), S.colptr)
+    newrowval = copy!(similar(S.rowval, TiNew), S.rowval)
+    return SparseMatrixCSC(S.m, S.n, newcolptr, newrowval, similar(S.nzval, TvNew))
+end
 
 function convert{Tv,Ti,TvS,TiS}(::Type{SparseMatrixCSC{Tv,Ti}}, S::SparseMatrixCSC{TvS,TiS})
     if Tv == TvS && Ti == TiS