I apologize if this has been answered before, I couldn't find it so far.
So how can Float64 be converted into ASCIIString?
My attempts
julia> parse(5.0)
ERROR: `parse` has no method matching parse(::Float64)
julia> convert(ASCIIString, 5.0)
ERROR: `convert` has no method matching convert(::Type{ASCIIString}, ::Float64)
in convert at base.jl:13
julia> parsefloat(5.0)
ERROR: `parsefloat` has no method matching parsefloat(::Float64)
Julia version 0.3.7
Use the string function:
julia> string(0.5)
"0.5"
EDIT:
For custom formatted strings, you can use the #sprintf macro:
julia> #sprintf("%.2f",0.5)
"0.50"
Related
I want to lock the type of a variable in Julia, how to do? For example, I define an array called weight,
weight = Array{Float64,1}([1,2,3])
Now I want to lock the type of weight as Array{Float64,1}, is it possible?
I mean if do not lock the type of weight, then if I mistakenly or casually do
weight = 1
Then weight will become an Int64 variable, so it is not longer a 1D array. This is obviously not what I want.
I just want to make sure that once I defined weight as 1D Float64 array, then if I change the type of weight, I want Julia gives me an error saying that the type of weight has been changed which is not allowed. Is it possible? Thanks!
This is useful because by doing this, it may preventing me from forgetting weight is an 1D array, and therefore preventing bugs.
For global variables use const:
julia> const weight = Array{Float64,1}([1,2,3])
3-element Vector{Float64}:
1.0
2.0
3.0
julia> weight[1]=11
11
julia> weight=99
ERROR: invalid redefinition of constant weight
Note that redefining the reference will throw a warning:
julia> const u = 5
5
julia> u=11
WARNING: redefinition of constant u. This may fail, cause incorrect answers, or produce other errors
You can circumvent it by using the Ref type:
julia> const z = Ref{Int}(5)
Base.RefValue{Int64}(5)
julia> z[] = 11
11
julia> z[] = "hello"
ERROR: MethodError: Cannot `convert` an object of type String to an object of type Int64
In functions use local with type declaration:
julia> function f()
local a::Int
a="hello"
end;
julia> f()
ERROR: MethodError: Cannot `convert` an object of type String to an object of type Int64
You'd normally write:
weight::Vector{Float64} = Array{Float64,1}([1,2,3])
...but this doesn't seem to be possible in global scope:
julia> weight::Vector{Float64} = Array{Float64,1}([1,2,3])
ERROR: syntax: type declarations on global variables are not yet supported
Stacktrace:
[1] top-level scope
# REPL[8]:1
However, you can do it in local scope or in a struct:
julia> function fun()
weight::Vector{Float64} = Array{Float64,1}([1,2,3])
weight = 1
end
fun (generic function with 1 method)
julia> fun()
ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type Vector{Float64}
Closest candidates are:
convert(::Type{T}, ::AbstractArray) where T<:Array at array.jl:532
convert(::Type{T}, ::LinearAlgebra.Factorization) where T<:AbstractArray at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.6/LinearAlgebra/src/factorization.jl:58
convert(::Type{T}, ::T) where T<:AbstractArray at abstractarray.jl:14
...
Stacktrace:
[1] fun()
# Main ./REPL[10]:3
[2] top-level scope
# REPL[11]:1
You could use const, but then redefinition with a value of the same type will cause a warning:
julia> const weight = Array{Float64,1}([1,2,3]);
julia> weight = [2.]
WARNING: redefinition of constant weight. This may fail, cause incorrect answers, or produce other errors.
1-element Vector{Float64}:
2.0
I am converting a code in julia 0.6 to 1.2.
Here is the old version:
#variable(model, use[i=eachindex(n), j=1:m], Bin)
Used = [indmax(getvalue(use[i,j])
for j=1:m) for i=eachindex(n)]
I converted to the following,
#variable(model, use[i=eachindex(n), j=1:m], Bin)
JuMP.optimize!(model)
Used = [argmax(JuMP.value(use[i,j])
for j=1:m) for i=eachindex(n)]
but with error:
MethodError: no method matching keys(::Base.Generator{UnitRange{Int64},getfield(Main, Symbol("##261#266")){Int64,JuMP.Containers.SparseAxisArray{VariableRef,2,Tuple{Any,Any}}}})
Closest candidates are:
keys(!Matched::Core.SimpleVector) at essentials.jl:606
keys(!Matched::Cmd) at process.jl:963
keys(!Matched::BenchmarkTools.BenchmarkGroup) at /Users/shuaiwang/.julia/packages/BenchmarkTools/7aqwe/src/groups.jl:31
...
pairs(::Base.Generator{UnitRange{Int64},getfield(Main, Symbol("##261#266")){Int64,JuMP.Containers.SparseAxisArray{VariableRef,2,Tuple{Any,Any}}}}) at abstractdict.jl:132
_findmax(::Base.Generator{UnitRange{Int64},getfield(Main, Symbol("##261#266")){Int64,JuMP.Containers.SparseAxisArray{VariableRef,2,Tuple{Any,Any}}}}, ::Colon) at array.jl:2068
findmax(::Base.Generator{UnitRange{Int64},getfield(Main, Symbol("##261#266")){Int64,JuMP.Containers.SparseAxisArray{VariableRef,2,Tuple{Any,Any}}}}) at array.jl:2065
argmax(::Base.Generator{UnitRange{Int64},getfield(Main, Symbol("##261#266")){Int64,JuMP.Containers.SparseAxisArray{VariableRef,2,Tuple{Any,Any}}}}) at array.jl:2153
(::getfield(Main, Symbol("##260#265")){ScenarioGraph,JuMP.Containers.SparseAxisArray{VariableRef,2,Tuple{Any,Any}}})(::Int64) at none:0
iterate at generator.jl:47 [inlined]
collect at array.jl:606 [inlined]
The problem seems to be unrelated to JuMP. The fix to your code is:
Used = [argmax([JuMP.value(use[i,j]) for j=1:m]) for i=eachindex(n)]
(I have not tested the whole code as it was not complete)
And the core of the issue is that you are not allowed to use argmax on generators, you have to pass a collection that supports pairs to it, e.g.:
julia> argmax(i for i in 1:3)
ERROR: MethodError: no method matching keys(::Base.Generator{UnitRange{Int64},getfield(Main, Symbol("##15#16"))})
fails, but
julia> argmax([i for i in 1:3])
3
julia> argmax((1,2,3))
3
julia> argmax((a=1,b=2,c=3))
:c
julia> argmax(Dict(:a=>1,:b=>2,:c=>3))
:c
work
I am trying to take a string a = "99.99" and then convert it to be of type float. On top of that, I want to be able to convert a to an int as well. How can I do that? The built-in int() and float() functions don't appear to take strings.
julia> a = "99.99"
"99.99"
julia> float(a)
ERROR: MethodError: no method matching AbstractFloat(::String)
Closest candidates are:
AbstractFloat(::Bool) at float.jl:252
AbstractFloat(::Int8) at float.jl:253
AbstractFloat(::Int16) at float.jl:254
...
Stacktrace:
[1] float(::String) at ./float.jl:271
[2] top-level scope at REPL[2]:1
julia> Int(a)
ERROR: MethodError: no method matching Int64(::String)
Closest candidates are:
Int64(::Union{Bool, Int32, Int64, UInt32, UInt64, UInt8, Int128, Int16, Int8, UInt128, UInt16}) at boot.jl:710
Int64(::Ptr) at boot.jl:720
Int64(::Float32) at float.jl:700
...
Stacktrace:
[1] top-level scope at REPL[3]:1
Inspired by this post.
You can use the parse(::Type{T}, ::AbstractString) function, like so:
julia> parse(Float64, "1")
1.0
Is there a method to convert a string to Expr? I tried the following but it doesn't work:
julia> convert(Expr, "a=2")
ERROR: MethodError: Cannot `convert` an object of type String to an object of type Expr
This may have arisen from a call to the constructor Expr(...),
since type constructors fall back to convert methods.
julia> Expr("a=2")
ERROR: TypeError: Expr: expected Symbol, got String
in Expr(::Any) at ./boot.jl:279
parse doesn't work here anymore. Now you need Meta.parse:
eval(Meta.parse("a = 2"))
(As pointed out by Markus Hauschel in a comment.)
As Colin said, to convert to Expr (or Symbol) you use parse.
And then to evaluate the resulting Expr you use eval.
Both together:
julia> eval(parse("a = 2"))
2
Note that as of Julia 1.0, this no longer works. Generally if you want to be evaluating string expression in Julia 1.0 you should be using expressions all the way through, e.g. :(a=2)
julia> parse("a=2")
ERROR: MethodError: no method matching parse(::Expr)
julia> #show eval(:(a=2))
eval($(Expr(:quote, :(a = 2)))) = 2
2
I have a function, f. I want to add a method that takes any container of Strings. For example, I want to write a method that generates the following when needed:
f(xs::Array{String, 1}) = ...
f(xs::DataArray{String, 1}) = ...
f(xs::ITERABLE{String}) = ...
Is this possible to do in Julia's type system? Right now, I'm using a macro to write a specialized method when I need it.
#make_f(Array{String, 1})
#make_f(DataArray{String, 1})
This keeps things DRY, but it feels...wrong.
Can't you just use duck typing? I.e., just assume that you're feeding the function an object of the right type and throw an error if at some point e.g. you don't have a string in your iterable.
This should improve once you can really talk about iterables using traits; currently there is no iterable type. Scott's answer, for example, will not work with a tuple of strings, even though that is iterable.
E.g.
julia> f(x) = string(x...) # just concatenate the strings
f (generic function with 1 method)
julia> f(("a", "á"))
"aá"
julia> f(["a", "á"])
"aá"
julia> f(["a" "b"; "c" "d"]) # a matrix of strings!
"acbd"
At least in Julia 0.4, the following should work:
julia> abstract Iterable{T} <: AbstractVector{T}
julia> f{T<:Union{Vector{String},Iterable{String}}}(xs::T) = 1
f (generic function with 1 method)
julia> x = String["a", "é"]
2-element Array{AbstractString,1}:
"a"
"é"
julia> f(x)
1