I want to read the user input and store it as a Rational, whatever the type: integer, float ot rational. For instance:
5 --> store it as 5//1
2.3 --> store it as 23//10
4//7 --> store it as 4//7
At the moment I wrote the following:
a = convert(Rational,parse(Float64,readline(STDIN)))
which is fine if I input an integer, like 5.
But if I input 2.3, a stores 2589569785738035//1125899906842624
.
And if I input a fraction (whether in the form 4/7 or the form 4//7) I get an ArgumentError: invalid number format for Float64.
How to solve the Float&Rational problems?
One way is to parse the raw input to an Expr (symbols), eval the expression, convert it to a Float64 and use rationalize to simplify the rational generated:
julia> rationalize(convert(Float64, eval(parse("5"))))
5//1
julia> rationalize(convert(Float64, eval(parse("2.3"))))
23//10
julia> rationalize(convert(Float64, eval(parse("4/7"))))
4//7
julia> rationalize(convert(Float64, eval(parse("4//7"))))
4//7
rationalize works with approximate floating point number and you could specify the error in the parameter tol.
tested with Julia Version 0.4.3
Update: The parse method was deprecated in Julia version >= 1.0. There are two methods that should be used: Base.parse (just for numbers, and it requires a Type argument) and Meta.parse (for expressions):
julia> rationalize(convert(Float64, eval(parse(Int64, "5"))))
5//1
julia> rationalize(convert(Float64, eval(parse(Float64, "2.3"))))
23//10