I have a large amount of data for over a 20 year period that I need to sort and group. I have two columns right now, one with a date of the day the data was collected and the second with the collected data value. In some instances there were samples taken more than once a day so I have the same date multiple times in my first column. My goal is to perform an operation that would group all my data by date and report the max value for each day of data collection.
A pivot table is the tool you need. Select your data, Insert Pivot Table, put the date in the row field, put the data as a data field, then right-click the data and Subtotal by Max. This should do it.
For more info on pivot tables, check out this tutorial.