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kotlinlang

Hey Guys, I am looping and deleting the element from the same list in kotlin. So I am getting error so what is way of doing that.

```Exception in thread "main" java.util.ConcurrentModificationException
	at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1013)
	at java.base/java.util.ArrayList$Itr.next(ArrayList.java:967)
	at ChipDataKt.main(ChipData.kt:72)
	at ChipDataKt.main(ChipData.kt)```

```var categoryList: MutableList&lt;Categories&gt;? = null
fun main() {
    categoryList = categoriesList().toMutableList()
    categoryList?.add(0, Categories("0", "physical-ktm", listOf(SubTopic("1", "vivek"))))
    println("After Add")
    categoryList?.forEachIndexed { index, categories -&gt;
        println("$index index -&gt; $categories")
    }

    categoryList?.mapIndexed { index, categories -&gt;
        if(categories.subTopic?.firstOrNull()?.title == "vivek"){
            categoryList?.removeAt(index)
        }
    }
    println("After operation")
    categoryList?.forEachIndexed { index, categories -&gt;
        println("$index index -&gt; $categories")
    }
}```


```fun categoriesList() = listOf(
    Categories("21", "physical", listOf(SubTopic("1", "abc"), SubTopic("2", "bjhef"))),
    Categories("2211", "mind", listOf(SubTopic("1", "abc"), SubTopic("2", "bjhef"))),
    Categories("22131", "motorized", listOf(SubTopic("1", "abc"), SubTopic("2", "bjhef"))),
    Categories("2134124", "coordination", listOf(SubTopic("1", "abc"), SubTopic("2", "bjhef"))),
    Categories("211243", "animal-supported", listOf(SubTopic("1", "abc"), SubTopic("2", "bjhef"))),
)```


```data class Categories(
    val id: String? = null, val title: String? = null, val subTopic: List&lt;SubTopic&gt;? = null
)

data class SubTopic(
    val id: String? = null, val title: String? = null, var priceId: String? = null
)```


The error says it all. One of the fix is why not try using `filter`? E.g:
```val filteredCategoryList = categoryList?.filter { categories -&gt;
    categories.subTopic?.firstOrNull()?.title != "vivek"
}```

You cannot delete items while in a for loop. You need to use the `Iterator`‘s function <https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html|https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html>

A quick stackoverflow search would have helped you <https://stackoverflow.com/questions/223918/iterating-through-a-collection-avoiding-concurrentmodificationexception-when-re|https://stackoverflow.com/questions/223918/iterating-through-a-collection-avoiding-concurrentmodificationexception-when-re>