Find max value

I have output from upstream snap as
20190417
20190416
20190415
20190414
when passing this to a mapper to find max I am getting all the values as Maximum.
How to get one Max value and assign it to a parameter ?
image

If those are all documents, then you would use the Aggregate Snap to get the max across all of the documents in the stream. You can then use the output of that as one of the parameters passed to a child pipeline as a parameter.