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Here are a few ways, each of which operates upon the individual component associations.

Here are a few ways, each of which operates upon the individual component associations. In the following discussion, recall that when a key name is not a valid symbol we can write, for example, #["col_name"] instead of #col.

In many places the documentation also says that associations can be used in place of lists in many functions. It should come as no surprise that Association itself allows us to use an association in place of a list:

The documentation also frequently says that associations can be used in place of lists in many functions. It should come as no surprise that Association itself allows us to use an association in place of a list:

2017 Update: It has been observed that the shorter form is not explictly mentioned in the documentation for Association (as of V11.1, see comments 1 and 2 for example). The documentation does mention that lists are "flattened out":

<| {"x" -> 1, "y" -> 2} |>
(* <| "x" -> 1, "y" -> 2 |> *)

... and that all but the last occurrence of repeated keys are ignored:

<| {"x" -> 1, "y" -> 1}, "y" -> 2 |>
(* <| "x" -> 1, "y" -> 2 |> *)

In many places the documentation also says that associations can be used in place of lists in many functions. It should come as no surprise that Association itself allows us to use an association in place of a list:

<| <| "x" -> 1, "y" -> 2 |> |>
(* <| "x" -> 1, "y" -> 2 |> *)

<| <| "x" -> 1, "y" -> 1 |>, "y" -> 2 |>
(* <| "x" -> 1, "y" -> 2 |> *)

This last expression is the "shorter form" from above.

Notwithstanding that the documentation strongly suggests that the short form is valid, I agree with commentators that it would be better if the documentation explicitly discussed the construction.