[Tutor] Replacing a value in a list

[Alan Gauld]

On 14/08/2021 05:23, nzbz xx wrote:
> Assuming that when there are consecutive missing values, they should be
> replaced with adjacent valid values e.g [1,2,-999,-999,5] should give
> [1,2,2,5,5]. And given [1,-999,-999,-999,5], the middle missing value would
> take the average of index 1 & 3. This should get an output of [1, 2 , 2,
> 3.5, 5]. How should it be coded for it to solve from the outer elements
> first to the inner elements?

That still leaves the question of what happens when there are 4 or 5
blank pieces? For 4 you can duplicate the average, but what about 5?
Is there a point at which ou decide the data is too damaged to continue
and throw an error?

As for coding it I'd write a small helper function to find the
start/stop indices of the blanks (or the start and length if you prefer)

Something like:

def findBlanks(seq,blank=-999):
    start = seq.index(blank)
    end = start+1
    while seq[end] == blank:
        end+=1
    return start,end

 For the simple case of 3 blanks you can do

if start != 0:
   seq[start] = seq[start-1]
if end != len(seq)-1:
   end = seq[end+1]

gapsize = end-start
if gapsize >= 3:
   seq[start+1]=(seq[start]+seq[end])/2

Now what you do if end-start>3 is up to you.
And what you do if the gap is at the start or
end of seq is also up to you...

It's all in the specification.
What is supposed to happen? Once you know the
complete algorithm the code should practically
write itself.

-- 
Alan G
Author of the Learn to Program web site
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