add metadata to show method (#217)

src/Arrow.jl

@@ -93,6 +93,7 @@ include("eltypes.jl")
 include("table.jl")
 include("write.jl")
 include("append.jl")
+include("show.jl")
 
 const LZ4_FRAME_COMPRESSOR = LZ4FrameCompressor[]
 const ZSTD_COMPRESSOR = ZstdCompressor[]

src/show.jl

@@ -0,0 +1,37 @@
+# 2-arg show: show schema and list # of metadata entries if non-zero
+function Base.show(io::IO, table::Table)
+    ncols = length(Tables.columnnames(table))
+    print(io, "$(typeof(table)) with $(Tables.rowcount(table)) rows, $(ncols) columns,")
+    meta = getmetadata(table)
+    if meta !== nothing && !isempty(meta)
+        print(io, " ", length(meta), " metadata entries,")
+    end
+    sch = Tables.schema(table)
+    print(io, " and schema:\n")
+    show(IOContext(io, :print_schema_header => false), sch)
+    return nothing
+end
+
+# 3-arg show: show schema and show metadata entries adaptively according to `displaysize`
+function Base.show(io::IO, mime::MIME"text/plain", table::Table)
+    limit = get(io, :limit, false)::Bool
+    display_rows, display_cols = displaysize(io)
+    ncols = length(Tables.columnnames(table))
+    meta = getmetadata(table)
+    if meta !== nothing
+        display_rows -= 1 # decrement for metadata header line
+        display_rows -= min(length(meta), 2) # decrement so we can show at least 2 lines of metadata
+    end
+    print(io, "$(typeof(table)) with $(Tables.rowcount(table)) rows, $(ncols) columns, and ")
+    sch = Tables.schema(table)
+    print(io, "schema:\n")
+    schema_context = IOContext(io, :print_schema_header => false, :displaysize => (max(display_rows, 3), display_cols))
+    schema_str = sprint(show, mime, sch; context=schema_context)
+    print(io, schema_str)
+    display_rows -= (count("\n", schema_str) + 1) # decrement for number of lines printed
+    if meta !== nothing
+        print(io, "\n\nwith metadata given by a ")
+        show(IOContext(io, :displaysize => (max(display_rows, 5), display_cols)), mime, meta)
+    end
+    return nothing
+end

test/runtests.jl

@@ -15,6 +15,7 @@
 # limitations under the License.
 
 using Test, Arrow, Tables, Dates, PooledArrays, TimeZones, UUIDs, CategoricalArrays, DataAPI
+using Random: randstring
 
 include(joinpath(dirname(pathof(Arrow)), "ArrowTypes/test/tests.jl"))
 include(joinpath(dirname(pathof(Arrow)), "../test/testtables.jl"))
@@ -355,6 +356,35 @@ tbl = Arrow.Table(Arrow.tobuffer(t))
     @test eltype(tbl.col1) == VersionNumber
 end
 
+@testset "`show`" begin
+    table = (; a = 1:5, b = fill(1.0, 5))
+    arrow_table = Arrow.Table(Arrow.tobuffer(table))
+    # 2 and 3-arg show with no metadata
+    for outer str in (sprint(show, arrow_table),
+                sprint(show, MIME"text/plain"(), arrow_table))
+        @test length(str) < 100
+        @test occursin("5 rows", str)
+        @test occursin("2 columns", str)
+        @test occursin("Int", str)
+        @test occursin("Float64", str)
+        @test !occursin("metadata entries", str)
+    end
+
+    # 2-arg show with metadata
+    big_dict = Dict((randstring(rand(5:10)) => randstring(rand(1:3)) for _ = 1:100))
+    Arrow.setmetadata!(arrow_table, big_dict)
+    str2 = sprint(show, arrow_table)
+    @test length(str2) > length(str)
+    @test length(str2) < 200
+    @test occursin("metadata entries", str2)
+
+    # 3-arg show with metadata
+    str3 = sprint(show, MIME"text/plain"(), arrow_table; context = IOContext(IOBuffer(), :displaysize => (24, 100), :limit=>true))
+    @test length(str3) < 1000
+    # some but not too many `=>`'s for printing the metadata
+    @test 5 < length(collect(eachmatch(r"=>", str3))) < 20
+
+end
 end # @testset "misc"
 
 end