Custom iterator breaks on last row of a readdlm-loaded array

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@nalimilan is already working on this.

Since Oct 1, 2018.

  • #29458 by @nalimilan — open

Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
julia
Domain
data

Research direction

Start by running the provided Julia reproducer with DelimitedFiles.readdlm and the custom Base.iterate implementation. Compare the iterator output with the expected final row, then inspect the linked Julia issue and Discourse discussion. Done means determining whether the bug belongs in DelimitedFiles.jl and documenting or testing the correct behavior.

Written by the indexing model from the issue text.

Description

When using a custom iterator over an array created with readdlm, the last row is broken in Julia 1.0. Yes, I did test this with no warnings in 0.7. This behavior looks like a bug to me and possibly related to JuliaLang/julia#28763

using DelimitedFiles # for readdlm

mutable struct mytbl # a custom object
    source
    function mytbl(csvdata::Base.GenericIOBuffer)
        source = readdlm(csvdata, ',')
        source = convert(Array, source[2:end,:]) # clear the headers
        new(source)
    end
end

Base.length(it::mytbl) = size(it.source, 1)

function Base.iterate(it::mytbl, (el, i)=(it.source[1,:], 1))
   return i >= length(it) ? nothing : (el, (it.source[i + 1,:], i + 1))
end

# some sample data
TABLE_CAST = """id,height,age,name,occupation
1,10.0,1,string1,2012-06-15 00:00:00
2,10.1,2,string2,2013-06-15 01:00:00
"""

table =  mytbl(IOBuffer(TABLE_CAST))

[ row for row in table ]
# Returns: last element is #undef
# Expected: the last element is the second row

[ row[1] for row in table ]
# Returns:
[1, 239486056]
# Expected: [1, 2]

[ row[2] for row in table ]
# Returns:
[10.0, 1.18e-315]
# Expected: [10.0, 10.1]

Note that I've tested this with more elements, the last row is always..well, broken.

Further discussion and a workaround in https://discourse.julialang.org/t/last-row-is-broken-when-iterating-an-array/15696

Dominant language
Julia
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Forks
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