For lists and vectors, we can slice the sequence and take any portion we want.
How to do similar operations to map objects ?

For example, I have a list of map object,

```
(def plays [
        {:name "Burial",     :plays 979,  :loved 9}
        {:name "Eno",        :plays 2333, :loved 15}
        {:name "Bill",       :plays 979,  :loved 9}
        {:name "Magma",      :plays 2665, :loved 31}])

```

For each map, I want to slice off plays column, and add rate column with default value, what is the idiomatic way to do this ?