# Help with logical indexing

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Barry on 18 Dec 2020
Answered: Rishabh Mishra on 21 Dec 2020
Hi All,
i have a question about logical indexing.
I have an array of three columns called pressure. Firstly, i check for values < 1000 (low = pressure < 1000) and then i would like to give those values new RGB values [0.1, 0.5, 0.9] so i can create a RGB pressure map.
i tried pressure(low) = [0.1, 0.5, 0.9] but this obviously didnt work. pressure(low) = 0.9 is working but is not the prefered outcome.
Any idead how this might work? Or do i have apply every column seperately like this: pressure(low, 1) = 0.1, pressure(low, 2) = 0.5 ... and so on?
Regards,
Barry
KALYAN ACHARJYA on 18 Dec 2020
"values < 1000 (low = pressure < 1000)"
• For for individual coloums or all columns have to satisfy
• How does you get thease R,G,B values 0.1, 0.5, 0.9
If you want help, then you need to make it easy to be helped.
:)

Rishabh Mishra on 21 Dec 2020
Hi,
You can use cell arrays (instead of double arrays) along with loop operations to work out the issue. Use the code below for the purpose,
% Pressure Matrix
pressure = [1101 450 987;1213 145 1997;148 1533 1420];
low = pressure < 1000;
RGB = {0.1 0.5 0.9};
% Convert Matrix to 2D Cell Array
pressure = num2cell(pressure);
% Replace Pressure values < 1000 by RGB cell
for k = 1:size(low,1)
for j = 1:size(low,2)
if low(k,j)
pressure{k,j} = RGB;
end
end
end
Hope this helps.

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