Add rownumber

Project.toml

@@ -1,7 +1,7 @@
 name = "DataAPI"
 uuid = "9a962f9c-6df0-11e9-0e5d-c546b8b5ee8a"
 authors = ["quinnj <quinn.jacobd@gmail.com>"]
-version = "1.14.0"
+version = "1.15.0"
 
 [compat]
 julia = "1"

src/DataAPI.jl

@@ -515,4 +515,11 @@ Throw an error if `x` does not support metadata deletion for column `col`.
 """
 function emptycolmetadata! end
 
+"""
+    rownumber(row)
+
+Return the row number of `row` in the source table.
+"""
+function rownumber end
+
 end # module

test/runtests.jl

@@ -93,6 +93,20 @@ end
 
 DataAPI.emptycolmetadata!(x::TestMeta) = empty!(x.col)
 
+# An example implementation of a table (without the Tables.jl interface)
+# for testing DataAPI.rownumber
+struct TestTable{T}
+    source::AbstractVector{T}
+end
+
+struct TestRow
+    source::TestTable
+    row::Int
+end
+
+Base.getindex(table::TestTable, row) = TestRow(table, row)
+DataAPI.rownumber(row::TestRow) = getfield(row, :row)
+
 @testset "DataAPI" begin
 
 @testset "defaultarray" begin
@@ -341,4 +355,11 @@ end
     @test isempty(DataAPI.colmetadatakeys(tm))
 end
 
+@testset "rownumber" begin
+    table = TestTable([(a=1,), (a=2,)])
+
+    @test DataAPI.rownumber(table[1]) == 1
+    @test DataAPI.rownumber(table[2]) == 2
+end
+
 end # @testset "DataAPI"