title: How to Disable Mat-Select Option once it has been selected
body: <p>I have a mat-select and I want to disable the options once I have selected them.
  For eg: If I select Time then Time should be disabled in the Next mat-select.
  I have created a stackblitz <a href="https://stackblitz.com/edit/angular-anus7w?file=app%2Fselect-overview-example.ts" rel="nofollow noreferrer">https://stackblitz.com/edit/angular-anus7w?file=app%2Fselect-overview-example.ts</a> of my requirement.Currently only the Key gets disabled. However in my case now the Drop down data will be dynamically generated and I cannot hard code the Values which need to be disabled.</p>
  <p>So what I want is that if I select a purticular value in mat-select 1 then that value should be disabled in mat-select 2. Similarly the value that I select</p>