Finding the Max/Min of Row/Col of an IDL Array

QUESTION: Is it possible to find the maximum (or minimun) in each row (or column) of a 2D array without using a FOR loop?

ANSWER: This answer was provided by Craig B. Markwardt on the IDL newsgroup in response to a question about finding the sum of a selected dimension of a multi-dimensional array.

I have also had the need for totalling over selective dimensions (sometimes more than one dimension), and also MIN/MAX.

Check out my IDL web page for CMAPPLY(), which can apply quite a number of operations to selected dimensions of an array. You can do this to more than one dimension at a time using a *list* of dimensions (similar to the DIMENSIONS parameter to MAKE_ARRAY or to REFORM).

http://astrog.physics.wisc.edu/~craigm/idl/idl.html

CMAPPLY supports more than just addition; it does:

   (+)   addition,        (*)   multiplication,
   (AND) logical AND,     (OR)  logical OR,
   (MAX) maximum, and         (MIN) minimum.

Where possible I avoid loops to improve performance, but your mileage may vary depending on the detailed use. (For example, for small arrays, your own loop may be faster).