Delete a value from NSMutable Array

Question

I have a NSMutableArray named _groupCategoryCurrentIds whose data is in this format

(
        {
        id = 2;
        name = Fashion;
    },
        {
        id = 5;
        name = Leisure;
    },
        {
        id = 14;
        name = Clothing;
    },
        {
        id = 17;
        name = Sports;
    },
        {
        id = 2;
        name = Fashion;
    },
        {
        id = 36;
        name = Men;
    },
        {
        id = 34;
        name = Woodland;
    },
        {
        id = 30;
        name = Accessories;
    },
        {
        id = 4;
        name = Entertainment;
    },
        {
        id = 40;
        name = Education;
    }
)

I'm trying to delete the object with id = 40 and this is how I do it

_groupCategoryCurrentIds = [[_groupCategoryCurrentIds filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"NOT id IN %@", @"40"]] mutableCopy];

But this deletes the object with id =4 as well. Any suggestion what I'm doing wrong?

Answer 1

Use

[NSPredicate predicateWithFormat:@"id != %@", @"40"]

or

[NSPredicate predicateWithFormat:@"id != %@", @40]

depending on whether the id is stored as a string or as a number.

Note that you can simplify your code to

[_groupCategoryCurrentIds filterUsingPredicate:...];

if _groupCategoryCurrentIds is a mutable array.

---

"IN" in a predicate is used for testing membership in an array or set, for example

[NSPredicate predicateWithFormat:@"NOT id IN %@", @[@40, @50]]

to get all objects where the id is neither 40 nor 50.

Using "IN" with a string on the right-hand side is not documented in the Predicate Programming Guide. It seems to behave like "is a substring of", so that in your case

[NSPredicate predicateWithFormat:@"NOT id IN %@", @"40"]

gives all objects where the id is not a substring of "40". That would explain your result. But again, this is not documented behaviour.