Matlab Fill previous value if missing value (or zero)
I have a vector containing a time series with different values and some missing values inbetween that are set to zero:
X=[0,0,2,0,5,0,0,0,4,0];
I want to create a new vector where the missing values (zeros) are populated by the previous value if one exist so that I get a new vector looking like:
Z=[0,0,2,2,5,5,5,5,4,4];
I have been browsing through the Matlab help and forums like this to find a neat and suitable function that would solve this for me with a one line solution or similar, but I have failed to do so. I can solve the problem开发者_JAVA技巧 through a few different steps according to below but I am guessing that there must be a better and easier solution available?
Current solution:
X=[0,0,2,0,5,0,0,0,4,0];
ix=logical(X);
Y = X(ix);
ixc=cumsum(ix);
Z=[zeros(1,sum(~logical(ixc))) Y(ixc(logical(ixc)))];
This does the trick, but it seems like an overly complicated solution to a simple problem, so can anyone help me with a better one? Thanks.
Here's a somewhat simpler version using cumsum:
X=[0,0,2,0,5,0,0,0,4,0];
%# find the entries where X is different from zero
id = find(X);
%# If we want to run cumsum on X directly, we'd
%# have the problem that the non-zero entry to the left
%# be added to subsequent non-zero entries. Thus,
%# subtract the non-zero entries from their neighbor
%# to the right
X(id(2:end)) = X(id(2:end)) - X(id(1:end-1));
%# run cumsum to fill in values from the left
Y = cumsum(X)
Y =
0 0 2 2 5 5 5 5 4 4
Here's a little something I wrote up. Does this do the trick?
% INPUT: the array you would like to populate
% OUTPUT: the populated array
function popArray = populate(array)
popArray = array;
% Loops through all the array elements and if it equals zero, replaces it
% with the previous element
%
% Since there is no element before the first to potentially populate it, this
% starts with the second element.
for ii = 2:length(popArray)
if array(ii) == 0;
popArray(ii)= popArray(ii-1);
end
end
disp(popArray);
Let me suggest another vectorized solution (though I like the one by @Jonas better):
X = [0 0 2 0 5 0 0 0 4 0]
id = find(X);
X(id(1):end) = cell2mat( arrayfun(@(a,b)a(ones(1,b)), ...
X(id), [diff(id) numel(X)-id(end)+1], 'UniformOutput',false) )
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