string - Julia:将数字字符串转换为 float 或 int

Question

我正在尝试将从数据库中提取的数字数据写入 Float64[] .原始数据在::ASCIIString格式，因此尝试将其推送到数组会出现以下错误:

julia> push!(a, "1")
ERROR: MethodError: `convert` has no method matching convert(::Type{Float64}, ::ASCIIString)
This may have arisen from a call to the constructor Float64(...),
since type constructors fall back to convert methods.
Closest candidates are:
  call{T}(::Type{T}, ::Any)
  convert(::Type{Float64}, ::Int8)
  convert(::Type{Float64}, ::Int16)
  ...
 in push! at array.jl:432

尝试直接转换数据不出所料会引发相同的错误:

julia> convert(Float64, "1")
ERROR: MethodError: `convert` has no method matching convert(::Type{Float64}, ::ASCIIString)
This may have arisen from a call to the constructor Float64(...),
since type constructors fall back to convert methods.
Closest candidates are:
  call{T}(::Type{T}, ::Any)
  convert(::Type{Float64}, ::Int8)
  convert(::Type{Float64}, ::Int16)
  ...

鉴于我知道数据是数字，有没有办法在推送之前转换它？

附言我正在使用版本 0.4.0

Answer 1

您可以 parse(Float64,"1")从一个字符串。或者在向量的情况下

map(x->parse(Float64,x),stringvec)

将解析整个向量。

顺便说一句，考虑使用 tryparse(Float64,x)而不是解析。它返回一个 Nullable{Float64}如果字符串不能很好地解析，则为 null。例如:

isnull(tryparse(Float64,"33.2.1")) == true

通常人们会想要一个默认值以防解析错误:

strvec = ["1.2","NA","-1e3"]
map(x->(v = tryparse(Float64,x); isnull(v) ? 0.0 : get(v)),strvec)
# gives [1.2,0.0,-1000.0]