Unable to do error view writing as the error record is not showing in preview

In that case, as I already said in my previous replies, use the typeof operator:

typeof $a == 'number'

I tried about typeof expression == ‘number’ in filter, I see some junk values in first column of final file instead of actual value.

Add $a != null to it. Like this:

typeof $a == 'number' && $a != null