[Jprogramming] replacing missing values with closest neighbor

[Lettow, Kenneth]

   NB. I have a sorted array

   sa=: 1 2 5 9

   

   NB. I want to expand this to an array of length (maxval+1)   

   rlen=: ((1&+)@(>./)) sa

   

   NB. I best picture the expanded array as: 

   ]exparray=: sa sa}(_$~rlen) 

_ 1 2 _ _ 5 _ _ _ 9

   

   NB. I want to replace the "blanks" above with the

   NB. nearest value in sa.  The desired result should be:

   

   desiredresult=: 1 1 2 2 5 5 5 5 9 9

   

   exparray,:desiredresult

_ 1 2 _ _ 5 _ _ _ 9

1 1 2 2 5 5 5 5 9 9

   

   NB. Where the first blank is replaced with the nearest value 1,

   NB. and the next blank is replaced with the nearest value 2 etc.

   

   NB. In the case of the blanks between 5 and 9, position 6

   NB. gets the value 5, postion 7 takes the lower value of 

   NB. the remaining values 5 and 9 (ties go to the lower value). 

   

   NB. I've been playing with this problem for a while and I am

   NB. not making any progress.  

   

   NB. Suggestions would be greatly appreciated.