Use jq command-line JSON processor to filter out a nested hash. See also: https://github.com/stedolan/jq/wiki/jq%20Cookbook

jq.sh

# http://stedolan.github.io/jq/

json='{"foo": {"genre":"deep house"}, "bar": {"genre": "progressive house"}, "baz": {"genre": "dubstep"}}'
echo "$json" | jq '[to_entries | .[] | select(.value.genre | contains("house"))] | from_entries'
# {
#   "bar": {
#     "genre": "progressive house"
#   },
#   "foo": {
#     "genre": "deep house"
#   }
# }

# To keep only N elements (2 here)
echo "$json" | jq 'to_entries | .[0:2] | from_entries'
# {
#   "bar": {
#     "genre": "progressive house"
#   },
#   "baz": {
#     "genre": "dubstep"
#   }
# }