Matching two array elements by rounding up and down

Dear mathworks community,

I need to create a conditional array that I find quite challenging. I uploaded an example data list and result that shows what I need to have at the end as both Excel file and txt file.

I have a reference list that is a column vector. It contains numbers from -10 to 10 with step size of 1 as in the uploaded file and I have a secondary list that contains numbers from -10 to 10 again, but the step sizes differ and list B can be shorter than list A. What I need to do is this:

I need to match the elements of two lists by rounding up or down the elements of list B and the below condition should apply:

if |listA(n) – listB(m)| < |listA(n) – listB(m+1)|

listA(n) matches with listB(m).

So each member of listA matches with the closest element of listB.

Also, if there is no closer value of listB(m) to listA(n), then, listB(m) can be used multiple times.

For example,

listA(n) = -5, listA(n+1) = -6 ,

listB(m) = -4.6, listB(m+1) = -5.2, listB(m+2) = -5.8 and listB(m+3) = -6.5

listA(n) - listB(m) = |-5-(-4.6)| = 0.4

listA(n) - listB(m+1) = |-5 – (-5.2)| = 0.2

since 0.2 < 0.4 listA(n) matches with listB(m+1)

and listA(n+1) - listB(m+2) = |-6 – (-5.8)| = 0.2,

listA(n+1) - listB(m+3) = |-6-(-6.5)| = 0.5

so listA(n+1) matches with listB(m+2)

Note: The difference between the elements of list A and list B can be greater than 1, still the same rule applies.

Note2: This is not a homework. I just need to calculate rms of the difference between reference list and secondary list.

Answer 1

[dpb]

fn='https://www.mathworks.com/matlabcentral/answers/uploaded_files/1359918/data_list.txt';
tT=readtable(fn);
ix=isfinite(tT.B);
tT.C=interp1(tT.B(ix),tT.B(ix),tT.A,'nearest','extrap')

tT = 21×3 table
     A       B        C  
    ___    _____    _____

    -10     -9.4     -9.4
     -9    -7.85     -9.4
     -8     -5.6    -7.85
     -7     -4.1    -7.85
     -6     -2.6     -5.6
     -5     -1.1     -5.6
     -4      0.4     -4.1
     -3      1.9     -2.6
     -2      3.4     -2.6
     -1      4.9     -1.1
      0      6.4      0.4
      1      7.9      0.4
      2      9.4      1.9
      3      NaN      3.4
      4      NaN      3.4
      5      NaN      4.9

[Cemre]

It really worked. Thank you so much!