concat
concat functions take 2 lists as a input and returns a new list
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## element
`element` function in TF is selects single element from a list.
hcl
element(concat(aws_vpc.generic.*.id, [""]), 0)
In above code, we have used `concat` and `element` both with using `element` we are just selecting the value at the 0th index in the list.
## flatten
`flatten` function in