import json
from numpy import mean, std


agg_functions = {
    #  'concat': lambda x: json.dumps(format_date_series(sorted(x))),
    "list": list,
    "concat2": lambda x: json.dumps([e for e in x]),
    "join": lambda x, delimiter: delimiter.join(x),
    "mean": mean,
    "std": std,
}
