Replacing n-d array elements based on pre-defined list

Hi,

Suppose I have an n-d array of q unique integers. I want to replace the value of every element in this n-d array based on a list (q by 2 matrix) like this:

1 k
2 l
3 m
...,

which means that every element with value 1 in the n-d array is replaced by k, every element with value 2 is replaced by l, etc. k, l, m... are double-precision numbers.

What's the most efficient way of doing this? Obviously, one could loop through 1, 2, 3..., find their linear indices and set elements with those indices to k, l, m... I would like to do this faster, if possible.

Any ideas are appreciated.

Answer 1

[Matt J]

 v=[k l m ...];
 X=...%Your n-D array of integers

 result = v(X);

[Pal]

Thanks!

Answer 2

[Roger Stafford]

If it isn't assumed that vector 'l' contains successive integers starting with 1, then you could do this:

 [tf,loc] = ismember(V(:),l);
 V(tf) = k(loc(tf));

where 'k' is the vector of values to replace those in 'l' and where 'V' is the n dimensional array. ('l' is the lowercase 'L', not the numeral.)

[Pal]

Thanks. You mean l(:,1), the integer elements, I presume.

[Roger Stafford]

My apologies. I misread your two vectors as being named 'l' and 'k'. My code still works whatever you name them provided they are the same length. It doesn't matter whether they contain integers or non-integers. Whenever an element in V is equal to one in 'l' (or whatever you call it,) it is replaced by the corresponding element in 'k' (or whatever you call that one.)