How to treat String as Array/Vector in Julia

Question

In Julia language, I want to use functions defined for Array{T,1} a.k.a. Vector{T} on a String, essentially treating it as Array{Char,1}.

An example of a function I would like to use:

julia> deleteat!("Hrello!",2)
ERROR: MethodError: no method matching deleteat!(::String, ::Int64)
Closest candidates are:
  deleteat!(::Array{T,1} where T, ::Integer) at array.jl:1177
  deleteat!(::Array{T,1} where T, ::Any) at array.jl:1214
  deleteat!(::BitArray{1}, ::Integer) at bitarray.jl:901
  ...
Stacktrace:
 [1] top-level scope at none:0

julia> deleteat!(['H','r','e','l','l','o','!'], 2)
6-element Array{Char,1}:
 'H'
 'e'
 'l'
 'l'
 'o'
 '!'

To be clear, I would like to start with a String and end up with a String, but use Array {Char,1} operations to alter the String.

That is a useful and well-illustrated question.

Julia Learner
– Julia Learner

2018-12-28 23:25:09 +00:00
Commented Dec 28, 2018 at 23:25 — Julia Learner
– Julia Learner, Commented Dec 28, 2018 at 23:25

Gnimuc · Accepted Answer · 2018-12-29 03:12:30Z

9

In Julia, one should always try collect firstly for getting a Vector from something else.

julia> deleteat!(collect("Hrello!"), 2)
6-element Array{Char,1}:
 'H'
 'e'
 'l'
 'l'
 'o'
 '!'

answered Dec 29, 2018 at 3:12

Gnimuc

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4 Comments

carstenbauer Over a year ago

You should probably mention that this is necessary because Strings are immutable.

Bogumił Kamiński Over a year ago

collect is the way to go (and I would normally use it). One could also add that actually you could write Vector{Char}(str) and Vector{UInt8}(str) to convert it to a mutable collection of character or code units. If you need a collection of code units that is read only then one can use a codeunits function.

dukereg Over a year ago

Good answer, but what is the inverse operation? I wasn't clear about this initially, but I want to end up with a String.

carstenbauer Over a year ago

@dukereg join should do the job.

Julia Learner · Accepted Answer · 2018-12-30 18:48:05Z

Strings can be split into Arrays and then operated on by using the split function.

For example, this could be done for your code above like this:

julia> deleteat!(split("Hrello!", ""), 2)
6-element Array{SubString{String},1}:
 "H"
 "e"
 "l"
 "l"
 "o"
 "!"

Edit

Since providing the above code example using split, I did the following benchmark comparison of collect vs. split for this problem.

The result is that collect is much faster (> 10X) than split as shown below.

julia> VERSION
v"1.0.3"

julia> using BenchmarkTools

julia> @benchmark deleteat!(split("Hrello!", ""), 2)
BenchmarkTools.Trial:
  memory estimate:  1.42 KiB
  allocs estimate:  26
  --------------
  minimum time:     748.396 ns (0.00% GC)
  median time:      804.819 ns (0.00% GC)
  mean time:        1.067 μs (20.80% GC)
  maximum time:     465.984 μs (99.71% GC)
  --------------
  samples:          10000
  evals/sample:     144

julia> @benchmark deleteat!(collect("Hrello!"), 2)
BenchmarkTools.Trial:
  memory estimate:  112 bytes
  allocs estimate:  1
  --------------
  minimum time:     60.299 ns (0.00% GC)
  median time:      65.431 ns (0.00% GC)
  mean time:        89.189 ns (20.99% GC)
  maximum time:     66.601 μs (99.83% GC)
  --------------
  samples:          10000
  evals/sample:     1000

@Gnimuc's advice to try collect first is definitely backed up by this benchmark.

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