How to create a map

I am new to GoHugo

I have the following code:

{{ range .Data.Pages }}
{{ with .Params.category }}<button type="button" data-filter="{{ . }}">{{ end }}{{ .Params.category }}</button>
{{ end }}

but it will create for each category a button even if the category is already present
I would like to make a map ? with just the list of the filtered ( map ) category
how can I do it with hugo?

This worked for me: