How can I equate all values of one vector to another and get the value ? Please find the example below

If I have

dataA = [1,2,3,4,5,6,7,8,9];
dataB = [0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1];

I need to equate for example: 1 = 0.1, 2=0.2, 3=0.3 so that if I ask value(7) it should display 0.7

Thank you in Advance.

[Rik]

Will dataA always be a continuous vector starting at 1 and incrementing by 1? In that case you can already use dataB directly:

dataB(7)%returns 0.7

[Rakesh Yadav Kodari]

May be I asked question the other way I think it would be better by real values

If dataA = -496,-636,-52,175,-84,-248,-555,-423,34,-174

dataB = -0.399609375000000,-0.512402343750000,-0.0418945312500000,0.140991210937500,-0.0676757812500000,-0.199804687500000,-0.447143554687500,-0.340795898437500,0.0273925781250000,-0.140185546875000

Now here How can i equate the the value at -496 = -0.399609375000000 ? %the first value of A is equal to first value of B

[Rik]

If your data is already paired, what exactly do you want to do? Mathematically it doesn't really make sense to equate them, as they are not equal. What do you want to use this for? Maybe then we can help you solve that problem instead.

Answer 1

[Andrei Bobrov]

dataA = [-496,-636,-52,175,-84,-248,-555,-423,34,-174]';
dataB = [-0.399609375000000,-0.512402343750000,-0.0418945312500000,...
    0.140991210937500,-0.0676757812500000,-0.199804687500000,...
   -0.447143554687500,-0.340795898437500,0.0273925781250000,-0.140185546875000]';

x = [-636,-84,34];
[lo,ii] = ismember(x,dataA);
out = dataB(ii(lo));

[madhan ravi]

but ii(lo) is the same as ii right? Is there any specific reason behind it or? Because I have noted in many of your answers.

[Stephen23]

@madhan ravi: you are right, but only if all elements of x are members of dataA. Robust programming would not assume this, which is probably why Andrei Bobrov prefers ii(lo), thus allowing for non-member values without causing an error.

If a non-member value is unacceptable to the algorithm then it would still be better to use assert and write a specific error message, rather than just rely on the uninformative "Indices must be positive integers" that would occur otherwise.

[madhan ravi]

@Stephen Cobeldick: +1 really a good explanation , thank you!

Answer 2

[Jos (10584)]

You can use logical indexing, a very powerful tool in Matlab

tf = dataB == 7 
dataA(tf)

[Rakesh Yadav Kodari]

May be I asked question the other way I think it would be better by real values

If dataA = -496,-636,-52,175,-84,-248,-555,-423,34,-174

dataB = -0.399609375000000,-0.512402343750000,-0.0418945312500000,0.140991210937500,-0.0676757812500000,-0.199804687500000,-0.447143554687500,-0.340795898437500,0.0273925781250000,-0.140185546875000

Now here How can i equate the the value at -496 = -0.399609375000000 ? %the first value of A is equal to first value of B

[Jos (10584)]

You lost me ... but why not try this:

dataB(dataA = -496)

[Stephen23]

@Jos: I guess that should be with double equals:

dataB(dataA == -496)

[Jos (10584)]

yes, of course. Thanks for the correction, Stephen :-)