# General Usage

**URL:** https://discourse.julialang.org/c/usage/6.md?page=974

[Latest](https://discourse.julialang.org/latest.md) · [Categories](https://discourse.julialang.org/categories.md) · [Tags](https://discourse.julialang.org/tags.md)

**Page:** 975

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## [Extending Float64 Base.show](https://discourse.julialang.org/t/extending-float64-base-show/11265)

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**Author:** [@iwelch](https://discourse.julialang.org/u/iwelch)\
**Replies:** 4\
**Last updated:** [May 31, 2018, 1:08am UTC](https://discourse.julialang.org/t/extending-float64-base-show/11265 "2018-05-31T01:08:33Z")

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Dear julia experts—I would like to print very small numbers in terms of eps(Float64). Something like julia\> Base.show(io::IO, p::Float64) = print(io, (abs(p)\<1000\*eps(Float64)) ? sprintf("%.3feps", (p/eps(Flo…

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## [Julia packages as part of other repos](https://discourse.julialang.org/t/julia-packages-as-part-of-other-repos/11272)

<div class="topic-metadata">

**Author:** [@ExpandingMan](https://discourse.julialang.org/u/ExpandingMan)\
**Replies:** 2\
**Last updated:** [May 30, 2018, 8:50pm UTC](https://discourse.julialang.org/t/julia-packages-as-part-of-other-repos/11272 "2018-05-30T20:50:13Z")

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We are currently having a discussion about the possibility of moving the Julia arrow implementation into the main arrow repo, if the arrow people ultimately decide that they want that. Some of us have raised the concern…

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## [REPL arithmetic gives wrong result on first run](https://discourse.julialang.org/t/repl-arithmetic-gives-wrong-result-on-first-run/11274)

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**Author:** [@kimran](https://discourse.julialang.org/u/kimran)\
**Replies:** 6\
**Last updated:** [May 30, 2018, 9:26pm UTC](https://discourse.julialang.org/t/repl-arithmetic-gives-wrong-result-on-first-run/11274 "2018-05-30T21:26:33Z")

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REPL gives 2 different results for simple arithmetic calculation Gives came after running a bunch of complex, quantitative code I have not replicated it, nor tried due to lack of time So this is just to put out the…

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## [Issue with RData](https://discourse.julialang.org/t/issue-with-rdata/5748)

<div class="topic-metadata">

**Author:** [@pegger0709](https://discourse.julialang.org/u/pegger0709)\
**Replies:** 8\
**Last updated:** [May 30, 2018, 7:20pm UTC](https://discourse.julialang.org/t/issue-with-rdata/5748 "2018-05-30T19:20:52Z")

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Hello, I am using julia v0.6.0 on the server at work and having a problem loading RData files using the RData package. I ran the following: “”" using RData ResponseMatrix = load(“Dahaniel-DoOR.data-6436660/data/respo…

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## [Comparing with Python](https://discourse.julialang.org/t/comparing-with-python/11119)

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**Author:** [@tk3369](https://discourse.julialang.org/u/tk3369)\
**Replies:** 56\
**Last updated:** [May 30, 2018, 6:53pm UTC](https://discourse.julialang.org/t/comparing-with-python/11119 "2018-05-30T18:53:14Z")

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Not trying to spin up any controversy… but do we have a list about things that are better in Julia than Python and vice versa as of today? To have a productive discussion, I would think such list should contain items tha…

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## [Function signature doesn't match when using Union](https://discourse.julialang.org/t/function-signature-doesnt-match-when-using-union/11268)

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**Author:** [@bluesmoon](https://discourse.julialang.org/u/bluesmoon)\
**Replies:** 3\
**Last updated:** [May 30, 2018, 6:43pm UTC](https://discourse.julialang.org/t/function-signature-doesnt-match-when-using-union/11268 "2018-05-30T18:43:58Z")

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Using julia 0.6.3-pre.2 (built from git), I tried the following: julia\> foo\_bar{T\<:Union{AbstractString, Symbol}}(d::Union{Symbol, AbstractVector{T}}=AbstractString\[\]) = "OK" foo\_bar (generic function with 2 methods) j…

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## [Fontconfig error in Homebrew](https://discourse.julialang.org/t/fontconfig-error-in-homebrew/10848)

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**Author:** [@yakir12](https://discourse.julialang.org/u/yakir12)\
**Replies:** 3\
**Last updated:** [May 30, 2018, 6:32pm UTC](https://discourse.julialang.org/t/fontconfig-error-in-homebrew/10848 "2018-05-30T18:32:58Z")

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This has already been reported in two issues (229 and 230), but I was wondering if anyone has a work around or some suggestions on how to solve this. It would be useful to know how many people are affected by this, or ev…

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## [Pkg(3) Tutorial](https://discourse.julialang.org/t/pkg-3-tutorial/11249)

<div class="topic-metadata">

**Author:** [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Replies:** 14\
**Last updated:** [May 30, 2018, 3:34pm UTC](https://discourse.julialang.org/t/pkg-3-tutorial/11249 "2018-05-30T15:34:22Z")

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I know that up to now it probably wasn’t a priority, but it would be nice to have a simple tutorial for the package manager. I’ve seen a few discussions of its use so far, but it seems that a newbie would have a hard tim…

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## [Advice for structure](https://discourse.julialang.org/t/advice-for-structure/11260)

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**Author:** [@rveltz](https://discourse.julialang.org/u/rveltz)\
**Replies:** 2\
**Last updated:** [May 30, 2018, 2:58pm UTC](https://discourse.julialang.org/t/advice-for-structure/11260 "2018-05-30T14:58:27Z")

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Hi, I am working with couples of vectors x,p where the size of x (resp. p) is fixed. I thought about using mutable struct Cp{T} x::Vector{T} p::Vector{T} end However, I would like to overload the operators so tha…

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## [Units, errors and type display](https://discourse.julialang.org/t/units-errors-and-type-display/11220)

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**Author:** [@Raf](https://discourse.julialang.org/u/Raf)\
**Replies:** 28\
**Last updated:** [May 30, 2018, 9:47am UTC](https://discourse.julialang.org/t/units-errors-and-type-display/11220 "2018-05-30T09:47:42Z")

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So it finally happened, I ran out of terminal screen to scroll up through all the Unitful types and find what my error was. Before I look into changing the memory buffer on my terminal, or log everything to file, can we…

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## [Segfault during deserialize](https://discourse.julialang.org/t/segfault-during-deserialize/11256)

<div class="topic-metadata">

**Author:** [@jinliangwei](https://discourse.julialang.org/u/jinliangwei)\
**Replies:** 0\
**Last updated:** [May 30, 2018, 6:08am UTC](https://discourse.julialang.org/t/segfault-during-deserialize/11256 "2018-05-30T06:08:37Z")

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The problem has been resolved. It’s not related to Julia. I have a C++ program with Julia embedded. Basically, I have an object of type Vector{Dict{Int32 Int64}}. I serialized it in one process and send it to another p…

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## [Strange error in Travis build using nightly + macOS](https://discourse.julialang.org/t/strange-error-in-travis-build-using-nightly-macos/11252)

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**Author:** [@Ronis\_BR](https://discourse.julialang.org/u/Ronis_BR)\
**Replies:** 1\
**Last updated:** [May 30, 2018, 9:12am UTC](https://discourse.julialang.org/t/strange-error-in-travis-build-using-nightly-macos/11252 "2018-05-30T09:12:50Z")

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Hi guys! I am trying to build my package in Travis against nightly + macOS and I am getting the following error: ERROR: Pkg.Types.CommandError("The following package names could not be resolved:\\n \* SatelliteToolbox (n…

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## [Nested function logic](https://discourse.julialang.org/t/nested-function-logic/11251)

<div class="topic-metadata">

**Author:** [@e3c6](https://discourse.julialang.org/u/e3c6)\
**Replies:** 6\
**Last updated:** [May 30, 2018, 7:44am UTC](https://discourse.julialang.org/t/nested-function-logic/11251 "2018-05-30T07:44:56Z")

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Suppose I define the function f(x) as follows: function f(x) if true g(x) = 2x else g(x) = 3x end g(x) end To me it was very surprising that calling f(2) returns 6 inst…

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## [Pkg problems - Impossible to update packages and to install some of them](https://discourse.julialang.org/t/pkg-problems-impossible-to-update-packages-and-to-install-some-of-them/11182)

<div class="topic-metadata">

**Author:** [@tfk17lstm](https://discourse.julialang.org/u/tfk17lstm)\
**Replies:** 5\
**Last updated:** [May 30, 2018, 7:14am UTC](https://discourse.julialang.org/t/pkg-problems-impossible-to-update-packages-and-to-install-some-of-them/11182 "2018-05-30T07:14:13Z")

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Dear Julia users, I am so desperate, since last Friday I have been having troubles with almost all the packages that I wanted to install. First of all I was triying to update my packages and I get the following error. …

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## [Why this function is type unstable](https://discourse.julialang.org/t/why-this-function-is-type-unstable/11212)

<div class="topic-metadata">

**Author:** [@Chong\_Wang](https://discourse.julialang.org/u/Chong_Wang)\
**Replies:** 12\
**Last updated:** [May 30, 2018, 6:36am UTC](https://discourse.julialang.org/t/why-this-function-is-type-unstable/11212 "2018-05-30T06:36:59Z")

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I have a function here function egvalsbyed(m, α, β, l, ϵ0) nhos = 100 gs = 2.0 H = spzeros(Complex128, 2\*nhos, 2\*nhos) for i in 1:nhos H\[i, i\] += l^(-2)/m\*(i-1+1/2)-gs/(4\*m\*l^2) H\[i+nhos,…

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## [Strange warning with \`Pkg.test("LightGraphs")\`](https://discourse.julialang.org/t/strange-warning-with-pkg-test-lightgraphs/11255)

<div class="topic-metadata">

**Author:** [@anon94023334](https://discourse.julialang.org/u/anon94023334)\
**Replies:** 2\
**Last updated:** [May 30, 2018, 6:33am UTC](https://discourse.julialang.org/t/strange-warning-with-pkg-test-lightgraphs/11255 "2018-05-30T06:33:15Z")

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Any ideas on where to look? Julia 0.7 as of this evening. ┌ Warning: broadcast will default to iterating over its arguments in the future. Wrap arguments of │ type \`x::Noop\` with \`Ref(x)\` to ensure they broadcast as "s…

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## [\[ANN\] REPLTetris.jl](https://discourse.julialang.org/t/ann-repltetris-jl/11128)

<div class="topic-metadata">

**Author:** [@shorty66](https://discourse.julialang.org/u/shorty66)\
**Replies:** 11\
**Last updated:** [May 29, 2018, 8:00pm UTC](https://discourse.julialang.org/t/ann-repltetris-jl/11128 "2018-05-29T20:00:34Z")

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Hello there, I had some fun writing a little Tetris game which is playable in the Julia REPL. I welcome comments and pull requests! Here is the link to the repo: REPLTetris.jl

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## [Efficient memory allocation for large system of ODEs](https://discourse.julialang.org/t/efficient-memory-allocation-for-large-system-of-odes/11226)

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**Author:** [@swainarpit](https://discourse.julialang.org/u/swainarpit)\
**Replies:** 2\
**Last updated:** [May 29, 2018, 12:54pm UTC](https://discourse.julialang.org/t/efficient-memory-allocation-for-large-system-of-odes/11226 "2018-05-29T12:54:16Z")

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Hi, I have a system of differential equations that mimic the clonal population in an immune system. For whoever is curious, the problem definition can be found in the post: At present, I am simulating with a small nu…

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## [New iterate interface and type stability](https://discourse.julialang.org/t/new-iterate-interface-and-type-stability/11222)

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**Author:** [@krcools](https://discourse.julialang.org/u/krcools)\
**Replies:** 3\
**Last updated:** [May 29, 2018, 11:01am UTC](https://discourse.julialang.org/t/new-iterate-interface-and-type-stability/11222 "2018-05-29T11:01:14Z")

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I have a general question about the new iterate interface: it seems that it is inherently type unstable. What I understand from various posts on this topic is that the introduction of the new interface is accompanied wit…

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## [About WARNING: replacing module on @everywhere include](https://discourse.julialang.org/t/about-warning-replacing-module-on-everywhere-include/8881)

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**Author:** [@paalon](https://discourse.julialang.org/u/paalon)\
**Replies:** 2\
**Last updated:** [May 29, 2018, 2:42am UTC](https://discourse.julialang.org/t/about-warning-replacing-module-on-everywhere-include/8881 "2018-05-29T02:42:41Z")

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I have a question about warnings when I tried to use @everywhere include. # ParallelTest.jl module ParallelTest include("MyModule.jl") using Distributions export loop function hello() println("Hello") end funct…

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## [Future-proof elementwise array comparison](https://discourse.julialang.org/t/future-proof-elementwise-array-comparison/11181)

<div class="topic-metadata">

**Author:** [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Replies:** 1\
**Last updated:** [May 28, 2018, 8:35pm UTC](https://discourse.julialang.org/t/future-proof-elementwise-array-comparison/11181 "2018-05-28T20:35:24Z")

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In v0.7, thanks to #16401, julia\> \[1, 2, 3\] == 1:3 true but in v0.6.2 it is false. I am currently writing unit tests that make a lot of these comparisons, and I want it to work in both versions. Should I use all(a .== …

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## [Efficient heatmap/general data updating](https://discourse.julialang.org/t/efficient-heatmap-general-data-updating/11203)

<div class="topic-metadata">

**Author:** [@Oz\_Wilson](https://discourse.julialang.org/u/Oz_Wilson)\
**Replies:** 2\
**Last updated:** [May 28, 2018, 6:53pm UTC](https://discourse.julialang.org/t/efficient-heatmap-general-data-updating/11203 "2018-05-28T18:53:28Z")

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I am making a gif of diffusion using a series of heatmaps, and come from a Matlab background. In that environment, it was far more efficient to directly set the z-data of a current plot instead of redrawing the plot afte…

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## [Invalid character \\exists](https://discourse.julialang.org/t/invalid-character-exists/11204)

<div class="topic-metadata">

**Author:** [@tpoisot](https://discourse.julialang.org/u/tpoisot)\
**Replies:** 1\
**Last updated:** [May 28, 2018, 5:36pm UTC](https://discourse.julialang.org/t/invalid-character-exists/11204 "2018-05-28T17:36:00Z")

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I was trying to create a new method, and apparently the \\exists character is invalid – despite the fact that it is suggested by auto-complete. Is this something normal, or is something wrong on my end? julia\> ∃ ERROR: s…

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## [Memory footprint is much larger than expected](https://discourse.julialang.org/t/memory-footprint-is-much-larger-than-expected/11157)

<div class="topic-metadata">

**Author:** [@jinliangwei](https://discourse.julialang.org/u/jinliangwei)\
**Replies:** 13\
**Last updated:** [May 28, 2018, 5:34pm UTC](https://discourse.julialang.org/t/memory-footprint-is-much-larger-than-expected/11157 "2018-05-28T17:34:32Z")

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docs = Vector{Tuple{Tuple{Int64, Int64}, Vector{Int32}}}(60000000) for i = 1:60000000 docs\[i\] = ((i, i), Vector{Int32}(2)) end while true end I reduced my problem to be above code. I expect docs to consume about 1.…

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## [Lapack Exception](https://discourse.julialang.org/t/lapack-exception/11190)

<div class="topic-metadata">

**Author:** [@maxtremblay](https://discourse.julialang.org/u/maxtremblay)\
**Replies:** 2\
**Last updated:** [May 28, 2018, 2:17pm UTC](https://discourse.julialang.org/t/lapack-exception/11190 "2018-05-28T14:17:10Z")

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Hello, After a search on Google, I can’t find the meaning of this error code. I understand that 0 means that everything is right, a negative number refers to the position of a wrong argument, but I can’t find the meani…

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## [UMFpackLU backslash operator involving multiple RHS](https://discourse.julialang.org/t/umfpacklu-backslash-operator-involving-multiple-rhs/11194)

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**Author:** [@ReidAtcheson](https://discourse.julialang.org/u/ReidAtcheson)\
**Replies:** 2\
**Last updated:** [May 28, 2018, 1:44pm UTC](https://discourse.julialang.org/t/umfpacklu-backslash-operator-involving-multiple-rhs/11194 "2018-05-28T13:44:33Z")

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Hello, I was experimenting with out-of-core linear solvers and found that most of my time was spent in computations of the form F\\x where F=lufact(A), A is a sparse matrix, and x is many column vectors. It seems a st…

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## [Trouble Speeding up Vectorized Functions with Parallelism](https://discourse.julialang.org/t/trouble-speeding-up-vectorized-functions-with-parallelism/11179)

<div class="topic-metadata">

**Author:** [@Juser](https://discourse.julialang.org/u/Juser)\
**Replies:** 12\
**Last updated:** [May 28, 2018, 10:45am UTC](https://discourse.julialang.org/t/trouble-speeding-up-vectorized-functions-with-parallelism/11179 "2018-05-28T10:45:12Z")

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I am running a 16-core machine and and trying to parallelize some simple vectorized code. As the simplest possible example, below is a piece of test-code in which I just try to parallelize the vectorized exp function. …

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## [Base.register\_taskdone\_hook crashes julia](https://discourse.julialang.org/t/base-register-taskdone-hook-crashes-julia/11196)

<div class="topic-metadata">

**Author:** [@tk3369](https://discourse.julialang.org/u/tk3369)\
**Replies:** 1\
**Last updated:** [May 28, 2018, 8:29am UTC](https://discourse.julialang.org/t/base-register-taskdone-hook-crashes-julia/11196 "2018-05-28T08:29:04Z")

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Am I using it correctly? This simple hook crashes julia in both 0.6 and 0.7. julia\> slow(n) = (sleep(n); rand()) slow (generic function with 1 method) julia\> t = @async slow(15) Task (runnable) @0x0000000112d3bcd0 ju…

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## [CSV misread](https://discourse.julialang.org/t/csv-misread/10966)

<div class="topic-metadata">

**Author:** [@tk3369](https://discourse.julialang.org/u/tk3369)\
**Replies:** 13\
**Last updated:** [May 28, 2018, 7:58am UTC](https://discourse.julialang.org/t/csv-misread/10966 "2018-05-28T07:58:35Z")

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How do I make it recognize the quotes? shell\> cat \> test.csv a,b,c,d,e,f 1863001,134,10000,1.0009,1.0000,-0.002033899 1863209,137,0,1.0000,"2,773.9000", julia\> CSV.read("test.csv") 2×6 DataFrames.DataFrame │ Row │ a …

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## [Options for working with SVN repo?](https://discourse.julialang.org/t/options-for-working-with-svn-repo/11174)

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**Author:** [@Crghilardi](https://discourse.julialang.org/u/Crghilardi)\
**Replies:** 4\
**Last updated:** [May 28, 2018, 6:33am UTC](https://discourse.julialang.org/t/options-for-working-with-svn-repo/11174 "2018-05-28T06:33:33Z")

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I have been working on a wrapper library for an established project hosted on Sourceforge. I reached out to the maintainers and they said they would welcome a contribution, so now I am trying to decide the best course of…

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