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Adding first, last and describe convenience functions. #42

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Adding first, last and describe convenience functions. #42

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0954b56
Adding implementation of `first`.
codetalker7 Aug 9, 2023
b2eab20
Adding spaces.
codetalker7 Aug 9, 2023
063c601
Making the last chunk dtable an `EagerThunk`.
codetalker7 Aug 11, 2023
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1 change: 1 addition & 0 deletions src/DTables.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ using Tables:
materializer,
partitioner,
rows,
rowtable,
schema,
Schema

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20 changes: 20 additions & 0 deletions src/table/dtable.jl
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Expand Up @@ -258,6 +258,26 @@ function length(table::DTable)
return sum(chunk_lengths(table))
end

function first(table::DTable, rows::UInt)
if nrow(table) == 0
return table
end

chunk_length = maximum(chunk_lengths(table))
num_full_chunks = Int(floor(rows / chunk_length)) # number of required chunks
sink = materializer(table.tabletype)
if num_full_chunks * chunk_length == rows
required_chunks = table.chunks[1:num_full_chunks]
else
# take only the needed rows from extra chunk
needed_rows = rows - num_full_chunks * chunk_length
extra_chunk = table.chunks[num_full_chunks + 1]
new_chunk = Dagger.@spawn sink(rowtable(fetch(extra_chunk))[1:needed_rows])
required_chunks = vcat(table.chunks[1:num_full_chunks], [new_chunk])
end
return DTable(required_chunks, table.tabletype)
end

function columnnames_svector(d::DTable)
colnames_tuple = determine_columnnames(d)
return colnames_tuple !== nothing ? [sym for sym in colnames_tuple] : nothing
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