Replace previous values with NaN

Question

MRINAL BHAUMIK 2021-3-21

回答： DGM 2021-3-21

采纳的回答： DGM

I have a vector with some numbers. if any of the number comes NaN then all the number before NaN will be NaN.

ex. A=[1 2 3 4 NaN 5 6 8 6]

then I want to get, A=[NaN NaN NaN NaN NaN 5 6 8 6]

Answer 1

DGM 2021-3-21

This can be done using isnan() and find():

A=[1 2 3 4 NaN 5 6 8 6 1 2 3 4 NaN 5 6 8 6];
nanidx=find(isnan(A),1,'last');
A(1:nanidx)=NaN

The result will be NaN up to the last instance of NaN in the original array:

A =
   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN     5     6     8     6

There might be some considerations to make if A ever becomes 2D, depending on how you want to handle things.