fix JuliaData/JuliaDB.jl#109

Author: Shashi Gowda

src/csv.jl

@@ -475,6 +475,7 @@ function guesscolparsers(str::AbstractString, header, opts::LocalOpts, pos::Int,
     guess = []
     prevfields = String[]
 
+    givenkeys = !isempty(colparsers) ? first.(collect(optionsiter(colparsers, header))) : []
     for i=1:nrows
         pos, _ = eatnewlines(str, pos)
         if pos > endof(str)
@@ -499,6 +500,9 @@ function guesscolparsers(str::AbstractString, header, opts::LocalOpts, pos::Int,
 
         # update guess
         for j in 1:length(guess)
+            if j in givenkeys
+                continue # user specified this
+            end
             if length(fields) != length(guess)
                 error("previous rows had $(length(guess)) fields but row $i has $(length(fields))")
             end

test/runtests.jl

@@ -419,6 +419,13 @@ import TextParse: _csvread
 
     # shouldn't fail because y doesn't exist
     @test _csvread("x\n1", colparsers=Dict("y"=>String)) == (([1],), ["x"])
+
+    # Don't try to guess type if it's provided by user. Issue JuliaDB.jl#109
+    s="""
+    time,value
+    "2017-11-09T07:00:07.391101180",0
+    """
+    @test _csvread(s, colparsers=Dict(:time=>String)) == ((String["2017-11-09T07:00:07.391101180"], [0]), String["time", "value"])
 end
 
 @testset "skiplines_begin" begin