Help with cusum and cellfun

Question

Stephen Thompson 2017-5-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/341032-help-with-cusum-and-cellfun

回答： Greg Dionne 2017-6-8

I am running the cusum function via cellfun as below - however I can only get one value from the output. When run separately, cusum outputs an [iupper,ilower] however running it via cellfun generates only one value, presumably the second change whether upper or lower. I am interested in first change - so either a way of getting that as an output or getting both as an output.

I hope this is clear. Thanks.

output = cellfun(@shift_time, input, 'UniformOutput', false);
function y = shift_time(x)
y = cusum(x, 100, 10, 0, 1);
end

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Walter Roberson 2017-5-19

This relates to https://www.mathworks.com/help/signal/ref/cusum.html

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2017-5-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/341032-help-with-cusum-and-cellfun#answer_267696

在 MATLAB Online 中打开

It would not be "the second change" that you got in that case: it would be the first output argument.

output = cellfun(@shift_time, input, 'UniformOutput', false);
function upper_lower = shift_time(x)
  [iupper, ilower] = cusum(x, 100, 10, 0, 1);
  upper_lower = {iupper, ilower};
end

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Stephen Thompson 2017-5-19

example_cusum.fig

That doesn't seem to be it - let me explain it again.

I have a 200X1 cell, each entry with 60000 points. Running cusum on one entry produces this (figure). There are two change point detection, upper and lower limits. In this case, it is the lower limit change point that I am interested in, the first detection, but the first detection might also be the upper limit change point in other data sets.

I want to replicate the cusum function across the whole dataset. It need not necessarily be via cellfun. The output will have to include both the upper and lower limits so that I can preserve both and later pick the first one.

I hope this is clear.

请先登录，再进行评论。

Answer 2

Greg Dionne 2017-6-8

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/341032-help-with-cusum-and-cellfun#answer_270075

在 MATLAB Online 中打开

I realize this may be a bit late, but in case someone else is looking for a solution, this worked for me:

% make some random data
a{1} = cumsum(randn(100,1));
a{2} = cumsum(randn(200,1));
a{3} = cumsum(randn(300,1));
a{4} = cumsum(randn(400,1));
a{5} = cumsum(randn(500,1));
% get first upper and lower breakouts
[iupper, ilower] = cellfun(@(x) cusum(x, 100,10,0,1), a, 'UniformOutput',false)
% get first breakout (if it exists)
ifirst = cellfun(@getfirst, iupper, ilower, 'UniformOutput',false)
function ifirst = getfirst(iupper, ilower)
if isempty(iupper)
    ifirst = ilower;
elseif isempty(ilower)
    ifirst = iupper;
elseif iupper < ilower
    ifirst = iupper;
else
    ifirst = ilower;
end
end

Output (you may get different results due to randn(), but hopefully they make sense)

iupper =
    1×5 cell array
      {0×1 double}    {0×1 double}    {[166]}    {[363]}    {0×1 double}
ilower =
    1×5 cell array
      {0×1 double}    {[31]}    {0×1 double}    {[189]}    {[43]}
ifirst =
    1×5 cell array
      {0×1 double}    {[31]}    {[166]}    {[189]}    {[43]}