UNIX for Dummies Questions & Answers

awk '
  FNR==1 {
    next                                          # skip the headers
  }

  FNR==NR {                                       # when reading the first file
    P[$1]=$2                                      # fill array P with points
    I[i++]=$1                                     # fill array I with point indices
    next
  }

  {
    while (j==0 || ($1>t && j+1 in I)) {          # determine if shift is needed to next index, do not shift beyond rightmost
      s=I[j]                                      # set s to next left index
      t=I[j+1]                                    # set t to next right index
      j++                                         # increase index
    }
    print $1, $2, P[s]+($1-s)*(P[t]-P[s])/(t-s)   # interpolate / extrapolate and print
  } 
' file2 file

752566 rs3094315 2.01296
752721 rs3131972 2.01314
753541 rs2073813 2.01413
760300 rs11564776 2.01695

awk '
FNR==NR && FNR >1 {
		    # Read first file starting from 2nd line
    		    A[$1]=$2
		    next
	          }
  
   NR!=1 && FNR==1{
		    # Reading 2nd file
		    # Sort Array index,print current line line
		    asorti(A,tmp)
		    print 
	          }

    NR!=1 && FNR>1{
			# This is index key
			key = $1

			# If exact match print as it is..
			if(key in A)
			{
				print key,A[key]
			}
	 		else
			{
				# No match search for upper and lower 
				for(i in tmp)
				{
				   if (tmp[i]>key)
				      { 
					x3 = tmp[i]
					break
				      }
				}

				x1 = tmp[i-1]

			# if x1 < x2 < x3 then interpolate 
			if(x1 < key && x3 >key)
				{

				   y1 = A[x1]
				   y3 = A[x3]
				   x2 = key
				   y2 = (y1+(x2-x1)*(y3-y1)/(x3-x1))

				   print x2,y2
				}
			else
				{
				   # print NaN as we cannot interpolate
				   print key,"NaN"
				}

		}
		
    	         }
    '  file2 file1

....
' OFMT='%.6f'  file2 file