How to map one array elements to another array elements?

I have an output array which shows to which feeder the animal goes in each trial for 6 trials. There could be only 4 feeders(1,2,3,4)

feederNum = [1 2 2 4 3 1]

The corresponding concentration of reward at the feeders are

feeder1 : 40, feeder2 : 30, feeder3: 20, feeder4: 10

I want to get the corresponding concentraions for the feederNum array. So my desired output is

conc = [40 30 30 10 20 40]

I am wondering if there is any key-value like feature to achieve this?

Answer 1

[Stephen23]

Method one: indexing:

num = [1,2,2,4,3,1];
val = [40,30,20,10];
out = val(num)

out = 1×6

40 30 30 10 20 40

Method two: interpolation:

out = interp1(val,num)

out = 1×6

40 30 30 10 20 40

[Struggling in MATLAB]

Thank you very much!

Answer 2

[dpb]

>> awardCoef=[-10,50];
>> conc=polyval(awardCoef,feederNum)
conc =
    40    30    30    10    20    40
>> 

More generically if isn't a polynomial (linear in this case) relationship, use lookup tables...

award=40:-10:10;
conc=award(feederNum);

Here award can be anything for each; just has to have a 1:1 entry to the number of values in feederNum -- and, of course the values of feederNum are from 1:numel(feederNum) since MATLAB arrays are one-based indexing.

If must change the numbering system to not be 1:N, then interp1 with the 'nearest' option can be used as the lookup table; same identical idea but not a direct array indexing operation.

[Struggling in MATLAB]

Thanks for your input!