If you just need to get the max value by the end of session (to increment a value or put at the bottom of a flat file ) you can do the following.
Let's say you need to find the max value for a port called INCOME. You feed rows through an expression. You create a new port that is either going to be local variable or output (depending what you want to do with it). Call it CURR_MAX and place it after the INCOME port. It will have the expression
IIF(CURR_VALUE>INCOME CURR_VALUE INCOME). That should do it.
Otherwise you either need to use a sorter which does caching anyway an Aggregator or do a lookup on the source you are reading from where the lookup override SQL calculates the max(for relational) or it you are reading from a relational DB like Oracle use an analytic function
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