How to substitute some of the values in a matrix

Hello all I have a matrix (748*6 double) including numbers and NaNs. The first column is test item numbers (defined already as ID) such as 1,3,5,7, etc, and the fourth column is the reaction times of participants (defined already as RT; 678, 467, etc). I need to replace some of the reaction times in this matrix. The new reaction times are in another matrix (defined already as RTc, 144*1 double) and I have the item numbers too (defined already as IDwords , 144*1 double). I wrote this code so that the reaction times in the old matrix would be substituted by the new reaction times. However, it does not work. I appreciate your help.

r=0;
for i=1:size(ID,1)
  for ii=1:size(ID,2)       
    if ID(i,ii)==IDwords;      
      RT(i,ii)=RTc;
      r=r+1;
    end        
  end
end

Answer 1

[dpb]

for i=1:size(ID,1)
  [inA,locB]=ismember(ID(i),IDwords);
  if inA      
    RT(inA)=RTc(locB);
  end        
end