# How to find consecutive numbers

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Edward on 2 Apr 2012
So i have an array: a=[16 17 32 33 48 63 79 80 81 97 98 113 114 129 130]
how can i write a program to find where those consecutive numbers are? i've tried using a for loop but haven't really got anywhere.. Please note that at one point there is 3 consecutive numbers.. The idea is each of these numbers is an index of another array: value=[3 0 2 5 3 2 1 0 0 2 7 7 3 7 8]; all equally spaced, which is supposed to mean: realvalue=[30 25 3 2 100 27 73 78]; and im trying to get the array 'realvaue' from arrays 'a' and 'value'

Thomas on 2 Apr 2012
diff(a)==1
should do the job for you. It will show you where in a you have consecutive values..
a(diff(a)==1)
Gives the first value
or
p=find(diff(a)==1)
q=[p;p+1];
a(q) % this gives all the pairs of consecutive numbers
ping pong on 13 Feb 2014
Edited: ping pong on 13 Feb 2014
working,its good

Andrei Bobrov on 2 Apr 2012
Edited: Andrei Bobrov on 27 Sep 2016
i1 = 1;
C{i1}=a(i1);
for j1 = 2:numel(a)
t = a(j1)-a(j1-1);
if t == 1
C{i1} = [C{i1} a(j1)];
else
i1 = i1 + 1;
C{i1} = a(j1);
end
end
OR
k= find(diff(a)==1);
k1 = [k;k+1];
idx = reshape(k1(k1~=intersect(k,k+1)),2,[]);
C = arrayfun(@(x)a(idx(1,x):idx(2,x)),1:size(idx,2),'un',0)
i1 = 1;
C(1)=1;
for j1 = 2:numel(a)
t = a(j1)-a(j1-1);
if t == 1
C(i1) = C(i1) + 1;
else
i1 = i1 + 1;
C(i1) = 1;
end
end
v = [3 0 2 5 3 2 1 0 0 2 7 7 3 7 8];
rv = str2double(mat2cell(sprintf('%d',v),1,C))
OR
k= find(diff(a)==1);
k1 = [k;k+1];
idx = reshape(k1(k1~=intersect(k,k+1)),2,[]);
id = sortrows([idx ones(2,1)*setdiff(1:numel(a),k1(:))].',1).';
C = diff(id)+1;
v = [3 0 2 5 3 2 1 0 0 2 7 7 3 7 8];
rv = str2double(mat2cell(sprintf('%d',v),1,C));
realvalue = accumarray(cumsum([true diff(a) ~= 1])',value',[],@(x)str2double(sprintf('%d',x')))
t = diff(a) == 1;
y = [t,false];
x = xor(y,[false,t]);
ii = cumsum(~(x|y) + y.*x);
out = accumarray(ii(:),value(:),[],@(z)10.^(numel(z)-1:-1:0)*z);
##### 2 CommentsShowHide 1 older comment
yeungor on 27 Oct 2016
Andrei definitely seems like a code golfer. Thanks for this, I'm using it to find linear regions in data.

Adil Sbai on 6 May 2017
Call this function:
function bool = successive(a)
% Determines if all the numbers in a given input 1D array are successive
% integers.
%
assert((size(a,1)==1 || size(a,2)==1) && isa(a,'double'));
a = sort(a);
bool = (abs(max(a)-min(a))+1)==numel(a);
end
These are examples:
>> successive([-1 4 3 0 2 1])
ans =
1
>> successive([-1 4 3 -3 2 1])
ans =
0