int, float or neither?

Question

Given a string, determine if it is an int, a float or neither.

Examples

• 123 - int
• 62727.0033 - float
• 644c.33 - neither

Your code should output a different value depending on which it is. For example it could return "i" for int, "f" for float and "n" for neither.

Details

The following are floats:

1.00 -0.0 1.0

The following are not floats:

 1e3 1.0ec3 -1e3 1e-3 1e+3 --1.0 +1.0 NaN 1.0.0 1. .1 -001.1

The following are ints:

42 -2 -0

The following are not ints:

042 00

In short, the rule for floats is that it is a sequence of digits following by a . followed by a sequence of digits. Optionally - is prepended. If it starts with 0 then the . must follow directly afterwards.

The rule for ints is that it is a sequence of digits where the first digit is not 0. The only exception is that 0 and -0 are ints.

Either sort of number can have - optionally prepended to it.

You can assume the input will only contain printable-ASCII.

Answer 1

APL (Dyalog Unicode), 46 39 bytes

Anonymous tacit prefix function. Returns 3 for float, 2 for int, and empty list for neither.

≢¨'^-?(0|[1-9]\d*)(\.\d+)?$'⎕S{⍵.Names}

Try it online!

Searches for the PCRE pattern ^-?(0|[1-9]\d*)(\.\d+)?$ then returns the name of the whole match and of each matched sub-pattern. Finally, the length of each (≢¨) list of names is returned. Since floats fill both sub-patterns, we get 3, while ints skip the last sub-pattern and thus give 2. Non-matches give an empty list.

Answer 2

Python 3.8 (pre-release), 87 bytes

lambda s:"-if"[getattr(re.match(r'-?(0|[1-9]\d*)(\.\d+)?$',s),'lastindex',0)]
import re

Try it online!

Straight-forward regular expression. Python wrapper feels a bit clumsy, though.

Returns 'i','f' and '-'. If we are ok with 1,2 and 0 instead that would save 7 bytes.

Details:

re.match only matches at the beginning, no ^ required. Annoyingly, Python returns two different object types, depending on whether there is a match or not. To work around this we use the cumbersome getattr which allows us to specify a fallback for non existent attributes.

Answer 3

Haskell, 95.. 61 bytes

f l=[1|(n,_)<-reads l,x<-["-0",show$round n],x==l||l==show n]

Try it online!

• As pointed out by @Peter Cordes there are floating point issues.
• Saved 18 Bytes by removing type hint to reads , thanks to @Unrelated String !
• Thanks to @Wheat Wizard for saving another 8 Bytes by applying do notation!
• Saved again 6 Bytes by @Wheat Wizard with a great use of list comprehension.

Returns:
[] = neither
[1] = Int
[1,1] = Float

We can return:
"" = neither
"1" = Int
"11" = Float
By adding 2Bytes and building a [Char] list instead of [Int].
Or an integer 0,1 or 2 by applying sum to the result for +3

f l uses list comprehension conditional trick :
If reads finds a number then we use (!) to determine its type.
If it fails it return an empty list , hence list comprehension is empty.

(!) compares value found with input reconverting it to string

We sum to get a consistent value for neither , we would get 0 or empty list

9 Bytes could be saved if we haven't to handle -0

Answer 4

QuadS, 31 bytes

Equivalent of my APL answer.

≢¨⍵
^-?(0|[1-9]\d*)(\.\d+)?$
⍵N

Try it online!

Answer 5

Retina 0.8.2, 35 bytes

^-?(0|[1-9]\d*)(?<1>\.\d+)?$|.+
$#1

Try it online! Link includes test cases. Outputs 2 for float, 1 for integer and 0 for everything else. Explanation:

^-?(0|[1-9]\d*)(?<1>\.\d+)?$|.+

Try to match an integer with an optional decimal fraction. Capture both the integer and the fraction (if it's present) in capture group 1. If the input is neither then simply match it all without capturing anything.

$#1

Output the number of captures of capture group 1.

Answer 6

PowerShell, 56 bytes

Takes a single number as a string; outputs 0 for other, 3 for integer, and 4 for float

("$args"-match"^-?(0|[1-9]\d*)(\.\d+)?$")+$matches.Count

Try it online!

PowerShell (Alternate Regex), 56 bytes

("$args"-match"^-?((?!0)\d+|0)(\.\d+)?$")+$matches.Count

Try it online!

Answer 7

Go, 135 bytes

package n
import."strconv"
func f(s string)byte{if _,e:=Atoi(s)
e==nil{return'i'}
if _,e:=ParseFloat(s,64)
e==nil{return'f'}
return'n'}

Go, 418 bytes

Some people have mentioned that the code above doesn't pass all test cases. I realized that the rules in the question don't actually match rules used by programming languages on what qualifies as an integer or float. For example, the rules say that 1e3 is not a float, but in reality it is:

package main

import (
   "fmt"
   "strconv"
)

func main() {
   f, err := strconv.ParseFloat("1e3", 64)
   fmt.Println(f, err) // 1000 <nil>
}

So I made an edit to handle these rules:

package n
import."strconv"
func f(s string)byte{if s[0]=='0'&&s[1]!='.'{return'n'}
if len(s)>=3&&s[:2]=="-0"&&s[2]!='.'{return'n'}
if s[0]=='-'{}else if s[0]>='0'&&s[0]<='9'{}else{return'n'}
if s[len(s)-1]>='0'&&s[len(s)-1]<='9'{}else{return'n'}
for _,r:=range s{if r=='-'{}else if r=='.'{}else if r>='0'&&r<='9'{}else{return'n'}}
if _,e:=Atoi(s);e==nil{return'i'}
if _,e:=ParseFloat(s,64);e==nil{return'f'}
return'n'}

Test:

package n

import (
   "fmt"
   "testing"
)

type testType struct {
   in string
   out byte
}

var tests = []testType{
   {"+1.0", 'n'}, {"--1.0", 'n'}, {"-0", 'i'}, {"-0.0", 'f'}, {"-001.1", 'n'},
   {"-1e3", 'n'}, {"-2", 'i'}, {".1", 'n'}, {"00", 'n'}, {"042", 'n'},
   {"1.", 'n'}, {"1.0", 'f'}, {"1.0.0", 'n'}, {"1.00", 'f'}, {"1.0ec3", 'n'},
   {"123", 'i'}, {"1e+3", 'n'}, {"1e-3", 'n'}, {"1e3", 'n'}, {"42", 'i'},
   {"62727.0033", 'f'}, {"644c.33", 'n'}, {"NaN", 'n'},
}

func TestNumber(t *testing.T) {
   for _, test := range tests {
      out := f(test.in)
      if out != test.out {
         fmt.Printf("%v %c %c\n", test.in, test.out, out)
      }
   }
}

Answer 8

Charcoal, 55 bytes

≔⁰ηＦＳ≡ι-≔∨¬η¹⁵η.≔⎇⊖↔⁻⁸η¹⁵¦⁵η0≔⎇›²η⁷｜⁸ηη≔｜⁹⎇Σιη⁶η§00121η

Try it online! Link is to verbose version of code. Outputs 2 for float, 1 for integer and 0 for everything else. Explanation: Implements a state machine (see below).

≔⁰η

Start in state 0.

ＦＳ≡ι

Switch over the input string's characters.

-≔∨¬η¹⁵η

- transitions from state 0 to state 1 and from any other state to state 15.

.≔⎇⊖↔⁻⁸η¹⁵¦⁵η

. transitions from states 7 or 9 to state 5 and from any other state to state 15.

0≔⎇›²η⁷｜⁸ηη

0 transitions from states 1 or 2 to state 7 and from any other state to the result of a bitwise OR with 8.

≔｜⁹⎇Σιη⁶η

Any other digit transitions by the result of a bitwise OR with 9 and any other character transitions to state 15 (obtained via a bitwise OR of 6 with 9).

§00121η

Look up the acceptance value of the final state, modulo 5. State 13 is reached for floats. State 7 is reached for 0 and state 9 is reached for other integers. States 0, 1, 5 and 15 cover everything else. Transition table:

	-	.	0	\d	X	Pattern
0	1	15	7	9	15	^
1	15	15	7	9	15	^-
5	15	15	13	13	15	^-?(0|[1-9]\d+)\.
7	15	5	15	15	15	^-?0
9	15	5	9	9	15	^-?[1-9]\d+
13	15	15	13	13	15	^-?(0|[1-9]\d+)\.\d+
15	15	15	15	15	15

Answer 9

Mathematica, 93 bytes

 Which[#~(a=StringMatchQ)~(b=RegularExpression)[c="-?([1-9]\\d*|0)"],0,#~a~b[c<>"\\.\\d+"],1]&

Which, being Mathematica's if-elseif chain. Just tests if the argument matches a regular expression for ints, then floats, all wrapped up in a lambda / pure function.

0 = int
1 = float
Null = neither

Mathematica, 81 bytes

Using the "a different value" Mathematica is fine returning complex symbols:

 #~(a=StringMatchQ)~(b=RegularExpression)[c="-?([1-9]\\d*|0)"]-#~a~b[c<>"\\.\\d+"]&

Parenthesis and square brackets remain for order of operations.

-False + True = int
False - True = float
0 = neither