How can I test if an input value is an integer?

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Hung Chu
Hung Chu 2017-2-21
回答： Weimin Zhang 2023-2-23
I want to know how to test whether an input value is an integer or not. I have tried using the function isinteger, but I obtain, for example, isinteger(3) = 0. Apparently, any constant is double-precision by Matlab default, and is therefore not recognized as an integer. Can anyone tell me what function I'm supposed to use?
  2 个评论
Torsten
Torsten 2017-2-21
Please explain in further detail the reason why you want to perform the test.
Best wishes
Torsten.
Hung Chu
Hung Chu 2017-2-21
For the function I'm trying to write, if any input of the function is not an integer, the function returns an error.

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采纳的回答

James Tursa
James Tursa 2017-2-21
E.g.,
>> isaninteger = @(x)isfinite(x) & x==floor(x)
isaninteger =
@(x)isfinite(x) & x==floor(x)
>> isaninteger(3)
ans =
1
>> isaninteger(3.1)
ans =
0
>> isaninteger(inf)
ans =
0
>> isaninteger(nan)
ans =
0
>> isaninteger(uint8(4))
ans =
1
>> isaninteger([-inf -1.2 0 1.3 5 inf nan])
ans =
0 0 1 0 1 0 0
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显示 1更早的评论
tqml
tqml 2020-10-30
I think using equal with floating point values might be error prone.
> mod((1:5)+eps,1)==0
ans =
1×5 logical array
0 1 1 1 1
For double value eps should be aroung 1e-15, so small rounding errors could mess up the check.
Therefore it might be helpful to introduce an additional parameter to control the tolerance and only check if the result is CLOSE to zero (and not equal)
function [b] = is_integer_value(x, tolerance)
%IS_INTEGER_VALUE Returns true if the value is an integer
% Checks if x modulo 1 is close to 0.
if nargin < 2
tolerance = eps;
end
b = ( mod(x,1) < tolerance ) ;
end
Steven Lord
Steven Lord 2020-10-30
When you call the eps function with no inputs, it returns the distance from 1 to the next largest number.
The distance from (for example) 2 to the next largest number is greater than eps. When you call eps with an input, it returns the distances from the elements of the input to the next largest numbers.
>> x = 1:5;
>> y = x + eps;
>> y > x
ans =
1×5 logical array
1 0 0 0 0
>> z = x + eps(x);
>> z > x
ans =
1×5 logical array
1 1 1 1 1
You can see the value of eps for each element of x:
>> eps(x)
ans =
Columns 1 through 3
2.22044604925031e-16 4.44089209850063e-16 4.44089209850063e-16
Columns 4 through 5
8.88178419700125e-16 8.88178419700125e-16

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更多回答（5 个）

Jan
Jan 2017-2-21
编辑：Jan 2017-2-21
According to your comment and Guillaume's suggestion:
assert(mod(x, 1) == 0, '%s: X must be an integer', mfilename);
Or safe this as M-file:
function T = isIntegerValue(X)
T = (mod(X, 1) == 0);
end
And then:
if ~isIntegerValue(X)
error('%s: X must be an integer', mfilename);
end
Hung Chu
Hung Chu 2017-2-21
Thank you! It works! But I don't know why LOL :P Could you explain to me how that function handles works?
Adam
Adam 2017-2-21
I use e.g.
validateattributes( myInteger, { 'double' }, { 'scalar', 'integer' } )
for validating my input arguments. Not so useful if you want a boolean/logical returned though to do something with after, although you can catch the exception that gets thrown but its untidy and inefficient to do that.
randell mullally
randell mullally 2019-7-3
I needed the same thing. these answers are Blaah for me so here was my soloution.
clear;
clc;
A=[3.6,4,4.25,5,6.175,nan,inf];
SizeA=size(A);
B=zeros(SizeA);
for i=1:SizeA(1,2)
if A(i)/round(A(i))==1
B(i)=1;
end
end
AB=[A;B]
AB =
3.6000 4.0000 4.2500 5.0000 6.1750 NaN Inf
0 1.0000 0 1.0000 0 0 0
I suppose if you want to test just one at a time... and let y be the test subject.
y=5;
if y/round(y)==1
fprintf('%3g is an intiger!! hooray\n',y)
else
fprintf('%3g is not an intiger!! sorry\n',y)
end
5 is an intiger!! hooray
testing this with A yeilds good results.
clear;
clc;
A=[3.6,4,4.25,5,6.175,nan,inf];
SizeA=size(A);
B=zeros(SizeA);
for i=1:SizeA(1,2)
if A(i)/round(A(i))==1
B(i)=1;
end
y=A(i);
if y/round(y)==1
fprintf('%3g is an intiger!! hooray\n',y)
else
fprintf('%3g is not an intiger!! sorry\n',y)
end
end
AB=[A;B];
3.6 is not an intiger!! sorry
4 is an intiger!! hooray
4.25 is not an intiger!! sorry
5 is an intiger!! hooray
6.175 is not an intiger!! sorry
NaN is not an intiger!! sorry
Inf is not an intiger!! sorry
If you really really really like this, ALOT!
find me on linkedin and endorse my matlab skill.
www.linkedin.com/in/randell-mullally
Best of luck!
  1 个评论
Cris Luengo
Cris Luengo 2020-7-9
This does not work if the input is 0.
What is wrong with the other answers? They actually work!

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Weimin Zhang
Weimin Zhang 2023-2-23
For an array x, perhaps use this:
assert(~any(mod(x,1)),'x must have integer(s) only');
or a function allIntegers = @(x)~any(mod(x,1))
For example,
>> allIntegers([1,2,3])
ans = logical 1
>> allIntegers([1,2.5,3])
ans = logical 0

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