replacing values with nan does not work while other approaches work (nifti files)

Question

Marta litwinczuk 2020-1-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/501604-replacing-values-with-nan-does-not-work-while-other-approaches-work-nifti-files

回答： Steven Lord 2020-1-23

I have three very similar pieces of code that operate on two matrices. Firt two versions of the code work, while nan function does not and I am wondering why

Code aims to use indexes of chosen values in one matrix to remove elements of another. Specifically, I am working on neurological images and I am trying use a binary mask to remove non-brain space from another image.

Here is the code

% load the .nii result file (79x95x68 matrix)
PB = niftiread('/MATLAB Drive/Phonology 005.nii');
PB = PB(:);
% load a binary brain mask (79x95x68 matrix, 0 = non-brain space)
mask = niftiread("mask_overlap70_thr50.hdr","mask_overlap70_thr50.img");
mask = mask(:);
%% remove non-brain space from PB
% this method works and removes number of vector elements in half
PB(mask == 0) = []; 
% this method to replace values also works 
PB(mask == 0) = 5; % I can then drop values of 5 from PB
% this method does not work
PB(mask == 0) = nan; 

I have double checked for nan values with isnan which returned a vector of 0s

So why does my nan function not work? I have found this approach from the forums

Thank you for your help

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Answer 1

Steven Lord 2020-1-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/501604-replacing-values-with-nan-does-not-work-while-other-approaches-work-nifti-files#answer_411652

在 MATLAB Online 中打开

My suspicion is that PB is an array of one of the eight integer types. One of the things that page states about the integer types is "If you convert a NaN value into an integer class, the result is a value of 0 in that integer class."