remove first s and last t rows of a matrix containing NaN, leave lows in the middle containing NaN.

6 次查看（过去 30 天）
Jo
Jo 2014-12-4
回答： C.J. Harris 2014-12-4
I have a Tx2 Matrix A and I would like to remove the rows in the beginning and in the end that contain any NaN. For example:
A=[[NaN;NaN;NaN;4;1;NaN;5;6;8;NaN;NaN],[NaN;NaN;2;7;6;5;NaN;6;18;2;NaN]]
should the equal to:
A=[[4;1;NaN;5;6;8],[7;6;5;NaN;6;18]]
many thanks for your help, Jo.

请先登录，再回答此问题。

采纳的回答

Thorsten
Thorsten 2014-12-4
There might be smarter solutions to figure out the indices of leading and trailing 1's in nanflag, but this solution works:
A=[[NaN;NaN;NaN;4;1;NaN;5;6;8;NaN;NaN],[NaN;NaN;2;7;6;5;NaN;6;18;2;NaN]];
nanflag = isnan(sum(A'));
ind = []; for i = 1:numel(nanflag), if nanflag(i) == 1, ind = [ind i]; else break, end, end
for i = numel(nanflag):-1:1, if nanflag(i) == 1, ind = [ind i]; else break, end, end
Anew = A(setdiff(1:size(A,1), ind), :);

更多回答（2 个）

Guillaume
Guillaume 2014-12-4
A=[[NaN;NaN;NaN;4;1;NaN;5;6;8;NaN;NaN],[NaN;NaN;2;7;6;5;NaN;6;18;2;NaN]];
removestart = logical(sum(cumprod(isnan(A)), 2));
removeend = flipud(logical(sum(cumprod(flipud(isnan(A))), 2)));
A(removestart | removeend, :) = []
  3 个评论
显示 1更早的评论
Guillaume
Guillaume 2014-12-4
编辑：Guillaume 2014-12-4
Works fine on R2014b, which version are you using?
In any case if cumprod does not accept logical, just convert them to double:
A=[[NaN;NaN;NaN;4;1;NaN;5;6;8;NaN;NaN],[NaN;NaN;2;7;6;5;NaN;6;18;2;NaN]];
nanpos = double(isnan(A));
removestart = logical(sum(cumprod(nanpos), 2));
removeend = logical(sum(cumprod(nanpos, 'reverse'), 2));
A(removestart | removeend, :) = []
I've also simplify the calculation of removeend. I didn't realise that cumprod had a reverse option.
Shame you accepted a less efficient code.
Jo
Jo 2014-12-4
I am using R2012b, this may be the cause. For anyone having the same version, adding double(..) helps, this adapted code works for me:
A=[[NaN;NaN;NaN;4;1;NaN;5;6;8;NaN;NaN],[NaN;NaN;2;7;6;5;NaN;6;18;2;NaN]];
nanpos = double(isnan(A));
removestart = logical(sum(cumprod(nanpos), 2));
removeend = flipud(logical(sum(cumprod(flipud(nanpos)), 2)));
A(removestart | removeend, :) = []
Thanks a lot!

请先登录，再进行评论。

C.J. Harris
C.J. Harris 2014-12-4
Nobody should ever need more than one line:
A = [[NaN;NaN;NaN;4;1;NaN;5;6;8;NaN;NaN],[NaN;NaN;2;7;6;5;NaN;6;18;2;NaN]];
A2 = A(find(~any(isnan(A),2),1,'first'):find(~any(isnan(A),2),1,'last'),:);

类别

在 Help Center 和 File Exchange 中查找有关 Logical 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by