Hello;
I'm not familiar with your previous question, however, in case you need to grab just a portion of a waveform, which is into an array, you first need to isolate the array element correspondent to the waveform you need, and then apply the method you mentioned.
You can use the Array Index.vi to grab a specific element of the array. That vi is on the Array subpallet.
Hope this helps.
Filipe A.
Applications Engineer
National Instruments