Set specific values to NaN

2017 4 13
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更新时间：2020 10 19
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Hello everyone
My problem is as follows. I have a matrix like this for example:
A = [1 2 3 4 5 6 6 6 6;
2 4 3 5 4 6 7 7 7;
5 4 4 4 3 7 8 8 8;
2 1 3 3 3 3 3 3 5]'
Now i want to get a matrix which deletes the values which are similar (starting with the second) untill the end of the column. So columns 1, 2, 3 should delete some values while column 4 shouldn't delete any numbers.
At the end the matrix should look like this
A = [1 2 3 4 5 6 NaN NaN NaN;
2 4 3 5 4 6 7 NaN NaN;
5 4 4 4 3 7 8 NaN NaN;
2 1 3 3 3 3 3 3 5]'
I hope you get my problem. Thanks in Advance.

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Peter Strassmann
Peter Strassmann 2020-10-19
编辑：Peter Strassmann 2020-10-19
Be aware that NaN values are only defined for data with single or double precision! It is resets integers to zero, e.g. uint8, int8.
rng(1);
A=randi([0,8], [100,1], "int8");
%A=double(A);
A(A>2)=nan;
If you want to associate NaN values to such data, you have to convert them first (before the remapping) with single(A) or double(A) into values with the according precision.

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Stephen23
Stephen23 2017-4-13
编辑：Stephen23 2017-4-14

1 个投票

>> A = [1,2,5,2;2,4,4,1;3,3,4,3;4,5,4,3;5,4,3,3;6,6,7,3;6,7,8,3;6,7,8,3;6,7,8,5];
>> idx = cumprod(double(diff(flipud(A))==0),1);
>> idx(end+1,:) = false;
>> idx = logical(flipud(idx));
>> A(idx) = NaN
A =
1 2 5 2
2 4 4 1
3 3 4 3
4 5 4 3
5 4 3 3
6 6 7 3
NaN 7 8 3
NaN NaN NaN 3
NaN NaN NaN 5

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Sascha Winter
Sascha Winter 2017-4-13
Thanks for your answer. It works for this matrix but it doesn't work for columns where all positions are NaN, because i get the error code: Error using logical NaN's cannot be converted to logicals. Do you have an idea how to pass this problem?
Stephen23
Stephen23 2017-4-14
编辑：Stephen23 2017-4-14
@Sascha Winter: how would you get a complete column of NaNs? As far as I can tell, if all elements in a column have the same value then following the description in your question "...starting with the second..." the first element would not be NaN. So how do you get a column of only NaNs?
>> A = [1,2,5,5;2,4,4,5;3,3,4,5;4,5,4,5;5,4,3,5;6,6,7,5;6,7,8,5;6,7,8,5;6,7,8,5]
A =
1 2 5 5
2 4 4 5
3 3 4 5
4 5 4 5
5 4 3 5
6 6 7 5
6 7 8 5
6 7 8 5
6 7 8 5
>> idx = cumprod(double(diff(flipud(A))==0),1);
>> idx(end+1,:) = false;
>> idx = logical(flipud(idx));
>> A(idx) = NaN
A =
1 2 5 5
2 4 4 NaN
3 3 4 NaN
4 5 4 NaN
5 4 3 NaN
6 6 7 NaN
NaN 7 8 NaN
NaN NaN NaN NaN
NaN NaN NaN NaN
Sascha Winter
Sascha Winter 2017-4-14
You understood my the wrong way. In my original matrix (318x7690) i have columns where all values are NaN. If you take the cumprod of columns where all values are NaN it isn't possible. The columns in my original matrix contain a lot of NaN's so the cumprod function will not work. I hope you get what i mean. I give you an example of how my matrix probably looks like.
A = [123456666; 344456621; NaNNaN2456666; 122222NaNNaNNaN; NaNNaNNaNNaNNaNNaNNaNNaNNaN]'
My matrix then should look like this
A = [123456NaNNaNNaN; 344456621; NaNNaN2456NaNNaNNaN; 12NaNNaNNaNNaNNaNNaNNaN; NaNNaNNaNNaNNaNNaNNaNNaNNaN]'
So rows 3.4 and 6 wouldn't work with this solution. Thanks im Advance for your help.
Stephen23
Stephen23 2017-4-14
Try this:
A = [1,2,3,4,5,6,6,6,6; 3,4,4,4,5,6,6,2,1; NaN,NaN,2,4,5,6,6,6,6; 1,2,2,2,2,2,NaN,NaN,NaN; NaN,NaN,NaN,NaN,NaN,NaN,NaN,NaN,NaN]'
idx = diff(flipud(A));
idx = cumprod(double(idx==0|isnan(idx)),1);
idx(end+1,:) = isnan(A(1,:));
idx = logical(flipud(idx));
A(idx) = NaN
which outputs this:
A =
1 3 NaN 1 NaN
2 4 NaN 2 NaN
3 4 2 NaN NaN
4 4 4 NaN NaN
5 5 5 NaN NaN
6 6 6 NaN NaN
NaN 6 NaN NaN NaN
NaN 2 NaN NaN NaN
NaN 1 NaN NaN NaN
Sascha Winter
Sascha Winter 2017-4-18
I think it works thanks a lot.

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