Extract the same elements in the array

Extract the same elements from Arr into a decimal group, and then place the decimal group in a large array of Dataarry

Nsmutablearray *arr =[nsmutablearray arraywithobjects:@ "1", @ "2", @ "1", @ "3", @ "2", @ "2", @ "4", @ "1", @ "2", @ "2", @ "2", @ "2" , nil];

1. Create an array Dataarry

Nsmutablearray *dataarr = [Nsmutablearray array];

2. Use two for loops to traverse arr

Method One,

for (Nsinteger i = 0; i<arr.count; i++) {

Nsmutablearray *temparr = [Nsmutablearray array];

NSString *str = Arr[i];

[Temparr ADDOBJECT:STR];

for (Nsinteger j = i+1; j<arr.count; j + +) {

NSString *tempstr = Arr[j];

if ([str isequal:tempstr]) {

[Temparr ADDOBJECT:TEMPSTR];

[Arr Removeobjectatindex:j]; Determine if two values are added to the Temparr, and then delete this element

}

}

[Dataarr Addobject:temparr];

}

Output result:dataarry:[[1,1,1],[2,2,2,2],[3],[2,2],[4],[2]]

The result is not what we want, the problem is that the number of elements in Arr will change, and the value of J is incremented in order, then we will see an error when judging by the element subscript.

Solution: 1, put the loop of J into reverse

for (Nsinteger j = arr.count-1; j>i; j--)

{　　　　　

}

2. Do not delete elements in the For loop, remove all elements from the entire Temparr array in arr outside of the For loop, and let i-1, always keep traversing from the beginning

　　　　　

for (Nsinteger i = 0; i<arr.count; i++) {

Nsmutablearray *temparr = [Nsmutablearray array];

NSString *str = Arr[i];

[Temparr ADDOBJECT:STR];

for (Nsinteger j = arr.count-1; j>i; j--) {

NSString *tempstr = Arr[j];

if ([str isequal:tempstr]) {

[Temparr ADDOBJECT:TEMPSTR];

}

}

[Dataarr Addobject:temparr];

if (temparr.count>1) {

[Arr Removeobjectsinarray:temparr];

I-=1;

}

NSLog (@ "dataarry:%@", Dataarr);

Extract the same elements in the array