To be more specific, we can use the sumOf() extension function with Int, Long, Double, UInt, ULong, BigInteger, and BigDecimal data types. So, there’s no need to have functions with different names for each data type, just like sumBy() and sumByDouble(). Despite that, we can also use this function with a list of Byte, Short, Long, and Float elements: val sumBy = numbers.sumBy )Īs shown above, we can use the same function to sum Int and UInt values and return Int and UInt summations, respectively. This function always returns an integer value. You may need to decipher that every time you come back to it.We can use the sumBy() function to find the sum of all values that are mapped by applying the selector function to each element in the collection. The indices/ mapIndexed-solution rather hide what's going on. It's way easier to read when you come back. And I can only recommend you to use the flatMap instead. Depending on how complex your condition is, the indices themselvses will not suffice you. Note that if what you are trying to insert is static, solution with the indices is of course easier then the mapping I've presented above. It should be easy enough though to add that case. indexOf returns -1 or itemsToInsertAfterMatch = null). what is matched with what? and what is inserted when where?).Īll the above solutions did not yet deal with the case when an element wasn't found (e.g. If you do not must (and who forces you?), I wouldn't use such a construct. As you said you iterate over the list, maybe a flatMap is rather something for you (in this example I add 'odd', 'even' after elements that are odd/even): val list = listOf('1', '2', '3', '4')Ġ -> listOf(it, ' listOf(it, ' itemsToInsertAfterMatch?.let

Kotlin for each with index