char to int?

[ggggg]

julia> parseint("4")
4

julia> parseint('4')
no method parseint(Char,)

julia> int('4')
52

So how do I turn '4' into 4? I feel like parseint should work, but maybe I'm just missing something.

[ggggg]

julia> a = '4'

'4'

julia> parseint("$a")

4

This works. Is this a good way?

[Jacob Quinn]

In  [2]: parseint(string('4'))

Out [2]: 4

Though I remember being a little baffled by this at first as well. I think my gotcha was trying to iterate over a string of numbers and each one was returning a Char, so trying to do any numeric operations was totally whack. I think the important thing here is to recognize that Char is is it's own type, with distinct behaviors from a String or Int (as opposed to just being a String subset).

-Jacob

[Kevin Squire]

Here's another solution (which only works if you know your characters are numbers):

julia> a = '4'
'4'

julia> a-'0'
4

Where are your chars coming from in the first place?

Kevin

[Stefan Karpinski]

Maybe parseint(::Char) should be the common locus for subtracting '0' and 'a' or 'A' or whatever. We have that logic repeated in a number of places around the system.

[ggggg]

I managed to wrap my head around char/string being different, which was a change from python. But I tried

julia> a = '4'

'4'

julia> String(a)

type cannot be constructed

Didn't think to try string. Thanks for the answers.  Kevin the numbers are coming from a string I'm parsing that represents a sudoku. I'm implementing a solver like Norvig's but using IntSets for fun.

I think I saw some discussion about how int and Int are confusing, and relics of when DataType wasn't a thing.  It seems that string and String are similar.

[Milan Bouchet-Valat]

Le mardi 26 novembre 2013 à 20:58 -0500, Stefan Karpinski a écrit :

Maybe parseint(::Char) should be the common locus for subtracting '0' and 'a' or 'A' or whatever. We have that logic repeated in a number of places around the system.

What do you mean?

I was going to suggest that parseint(::Char) should behave just like parseint(::String), and that int(::Char) should keep its current behavior. Reading the docs for parseint() and int(), it seems that the latter is intended mainly to convert between numbers, which seems consistent with the idea of getting the character code as an integer. (Though in this scenario, int(::String) should maybe not exist, to reduce confusion. Not sure.)


My two cents

[Stefan Karpinski]

I mean this:

parseint(c::Char) =

    '0' <= c <= '9' ? c-'0' :

    'a' <= c <= 'z' ? c-'a'+10 :

    'A' <= c <= 'Z' ? c-'A'+10 :

        error("invalid digit: $(repr(c))")

It's the only sensible definition if we're going to give this a meaning and it kind of makes sense to factor this out since it's used in a number of places.

[Jacob Quinn]

+1 to that definition Stefan. I think that's exactly what people would expect calling parseint on a Char.

-Jacob

[Stefan Karpinski]

Done: https://github.com/JuliaLang/julia/commit/77064c1bfc5bd5345970a5ce67568389440a7810.

[Milan Bouchet-Valat]

Le mercredi 27 novembre 2013 à 04:01 -0500, Stefan Karpinski a écrit :
> I mean this:
>
>
> parseint(c::Char) =
> '0' <= c <= '9' ? c-'0' :
> 'a' <= c <= 'z' ? c-'a'+10 :
> 'A' <= c <= 'Z' ? c-'A'+10 :
> error("invalid digit: $(repr(c))")
>
>
> It's the only sensible definition if we're going to give this a
> meaning and it kind of makes sense to factor this out since it's used
> in a number of places.

Ah, indeed, I hadn't thought about hexadecimal notation.