Insert NaN into specific values

I use this code to insert all the lines in column 4 the numbers equal to 0 equal to NaN, but nothing happens.

That is, I want to insert NaN in all numbers equal to 0 of all rows in column 4.

Does anyone have an idea?

s=load('spi_dca.mat');
spi_dca = s.spi_dca;
mask=spi_dca(:,4)==0;
spi_dca(mask,4)=spi_dca(mask,4)==NaN;

Answer 1

[Arif Hoq]

try this:

s=load('spi_dca.mat');
spi_dca = s.spi_dca;
col4=spi_dca(:,4);
col4(col4==0)=NaN;
output=[spi_dca(:,[1 2 3]),col4];

Answer 2

[Voss]

s=load('spi_dca.mat');
spi_dca = s.spi_dca;
mask=spi_dca(:,4)==0;
spi_dca(mask,4)=NaN;

[Augusto Gabriel da Costa Pereira]

magnificent!

the code worked perfectly.