calculating frequency in matlab

Hi. Ive calculated the spi index in matlab. And now I want to calculate the frequency (moderate, severe and strong) drought with gridded data as I want to plot the spatial in the form of frequency and severity. Thus, to calculate the frequency of each drought class (moderate, severe and strong) I have to define the spi value associated with each class and then take the frequency of values belonging to it. Can I do this in matlab? I have to have a predefined frequency in each class. Thank you in advance!

[KSSV]

You can use logical indexing. Also have a look on histogram.

[Nurul Ain Basirah Zakaria]

Can I use it on gridded data?

[KSSV]

Yes it can be used.