I have an array of objects which I am currently sorting by date (the objects each have a date field on them).
I want to be able to split up this array into multiple sections, where each section contains the objects that have the same date. Is there already a supported mechanism for this?
There seems to be no mechanism for this, other than the way I suggested in my comment:
I create a nsmutabledict, then I iterate over my sorted list of objects. For each object, I check the date, and see if there exists a key in my dict pertaining to that date. If so, I retrieve that value from the dict and append this object to that array. If not, I create a new list and insert it into the dict with the key pertaining to the date.
- (NSArray *)filteredArrayUsingPredicate:(NSPredicate *)predicate
will be useful. Write a predicate to get the filtered array of all the elements matching the date of the first item in the array. Add that array to a new mutable array, which is the object holding all the filtered arrays with matching dates.
Record that date as having been used. Iterate over the original array until you find a different date and repeat the filteredArrayUsingPredicate operation. Keep doing this until you have covered all unique dates in the array.
I was going to suggest using NSSet to remove all the items that have been filtered already to reduce processing time but the number of items may be important, and depending on the objects NSSet could discard duplicates.
An optimisation could be to use NSSet to non-destructively create a set of unique dates from the original array and then iterate over that set, performing the filteredArrayUsingPredicate operation. But whether that is practical depends on your data.
nsmutabledict to track dates, traverse sorted array, get date, see if date key exists in dict. If it does, append to the end of that key's value, else create a new dict key with a nsmutablearray as its value.