How do I pad the middle of an array?

I have an array that is basically stepped. I want to pad each side of the step with additional numbers (the orange cells). Can you help me figure out how to do this?

Original Array:

How I want it to be:

Answer 1

[DGM]

For vectors, you can just extrapolate each segment and cat them back together. You'd need to determine where each step is.

a=[1:6 78:82 109:111]'
b=[interp1(a(1:6),1:8,'linear','extrap'), ...
   interp1(a(7:11),-1:7,'linear','extrap'), ...
   interp1(a(12:14),-1:5,'linear','extrap')]'

gives:

a =
     1
     2
     3
     4
     5
     6
    78
    79
    80
    81
    82
   109
   110
   111
b =
     1
     2
     3
     4
     5
     6
     7
     8
    76
    77
    78
    79
    80
    81
    82
    83
    84
   107
   108
   109
   110
   111
   112
   113

[Amanda Beatty]

I'm struggling to understand what the 1:8 and -1:7 and -1:5 are. When I look up interp1 it looks like that would be the x value while the rest of the vector is the v value, but I don't have x values? How did you come up with those nubmers?

Also, I have an unknown number of steps. You wrote out "interp1" 3 times, but this is in a loop and each iteration might have a different number of steps, all of which are unknown. I don't know how to account for that.

Sorry I didn't clarify that in my original question.

[DGM]

Those second vectors specify the new query points. What's confusing is that the short syntax I used is basically using the vector length as "x" so to speak. So it's like doing this:

interp1(1:5,a(7:11),-1:7,'linear','extrap');

so I'm taking a 5-element vector and I'm extrapolating two elements off of either end.

Yeah, you wouldn't want to do that a bunch of times, but the idea is the same. The only hard part about doing it automatically is determining the criteria you're going to use to detect what you consider to be a step. For this example, I'm just going to assume a maximum difference.

clc
a=[1:6 78:82 109:111]'
ps=2; % specify a padsize

% i'm assuming that any increment >1 is considered a discontinuity
a=reshape(a,[1 numel(a)]); % safeguard against vector orientation
discloc=find(diff(a)>1); % find transitions
discloc=[discloc(1) diff([discloc numel(a)])] % find width of chunks
chunks=mat2cell(a,1,discloc); % split vector into subvectors

for c=1:numel(chunks)
	% you had chunk 1 padded asymmetrically
	% you can also pad the last chunk asymmetrically if you want
	if c==1
		indexvec=1:(numel(chunks{c})+ps);
	else
		indexvec=(1-ps):(numel(chunks{c})+ps);
	end
	chunks{c}=interp1(chunks{c},indexvec,'linear','extrap');
end
b=cell2mat(chunks)'

[Amanda Beatty]

@DGM Thank you thank you! This solution is so much more elegant than what I was trying (and failing) to do with interp1.