Comparing first n digits

Hi ,

I have two columns of numbers A and B. A is 9 digits and B is 8 digits. How can I find the row in B that matches A(i) in a loop (i=1:length(A))

[Walter Roberson]

What does it mean for a row in B to match in this case?

[wesso Dadoyan]

example A(2)=654356105 B is column vector that contains in row 20 number 65435610. B(20) matches A(2) since the first 8 digits of A(2)=B(20) how can I find row 20 in B?

[Rik]

I would recommend not using a loop. If you have stored the number in a number format, just divide the A by 10 and floor it to convert to 8 digits. If you have it as a string, just remove the last character.

Then you can use ismember to do the work. ismember can be slow, so looking for alternative methods can be worthwhile if that is the bottleneck in your code.

Answer 1

[Walter Roberson]

[tf, Bidx] = ismember(fix(A/10), B);

Now, tf(K) tells you whether A(K) had a match in B or not, and if tf(K) is true then Bidx(K) tells you which entry in B matched.