insert matrix index to specific number

11 vues (au cours des 30 derniers jours)
ByoungYong Ryu
ByoungYong Ryu le 3 Mar 2017
Modifié(e) : Stephen23 le 3 Mar 2017
I have zeros matrix A = zeros(1,10);
and I want insert specific number to index range.
ex) index = [1 6 10]; value = [4 6];
I want return the matrix ans = [4 4 4 4 4 4 6 6 6 6];
How can I return this answer not using 'for';

Réponses (3)

Andrei Bobrov
Andrei Bobrov le 3 Mar 2017
my small contribution
index = [1 6 10];
value = [4 6];
ii = zeros(index(end),1);
ii([1,index(2:end-1)+1]) = 1;
A = value(cumsum(ii));
  2 commentaires
Jan
Jan le 3 Mar 2017
+1: I'd prefer this and guess, it is the fastest solution.
Walter Roberson
Walter Roberson le 3 Mar 2017
This assumes that index(1) is 1.
It is an interesting approach, though.

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Walter Roberson
Walter Roberson le 3 Mar 2017
A(index(1):index(end)) = repelem( value, [index(2)-index(1)+1,diff(index(2:end))]);

Stephen23
Stephen23 le 3 Mar 2017
Modifié(e) : Stephen23 le 3 Mar 2017
For MATLAB versions without repelem (pre R2015a):
>> index = [1 6 10]; value = [4 6];
>> cell2mat(arrayfun(@(d,v)repmat(v,1,d),diff(index),value,'Uni',0))
ans =
4 4 4 4 4 6 6 6 6
  2 commentaires
Walter Roberson
Walter Roberson le 3 Mar 2017
Notice though that you output five 4's when the desired output is six 4's. The pattern appears to be that the first index gives a starting position number, that the next gives the ending position number of the first value, that the next after that gives the ending position number of the second value, and so on. The number of repeats of the first item is special, which is why I ended up using [index(2)-index(1)+1,diff(index(2:end))]
Stephen23
Stephen23 le 3 Mar 2017
Modifié(e) : Stephen23 le 3 Mar 2017
@Walter Roberson: thank you for fixing that strange inconsistency in the index definition. Applying your fix:
>> index = [1 6 10]; value = [4 6];
>> idx = [index(2)-index(1)+1,diff(index(2:end))];
>> cell2mat(arrayfun(@(d,v)repmat(v,1,d),idx,value,'Uni',0))
ans =
4 4 4 4 4 4 6 6 6 6

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