I would like to remove elements from a collection,...

# getting-started

[Daniele B]

I would like to remove elements from a collection, based on a condition.
For a list, we can use:

myList.removeAll { it.myField != myFieldValue }

But for a map, there doesn’t seem to be removeAll :

myMap.removeAll { it.key != myKeyValue }    <--- removeAll doesn't exist

what should I use instead?

[Luke]

Maybe myMap.filter { it.key == myKeyValue } ?

[Luke]

It creates a new map though

[Daniele B]

my map is defined as:

val myMap : MutableMap<Int, MyObject>

so, being a val, a new map cannot be set

[ilya.gorbunov]

myMap.keys.removeAll { it != myKeyValue }

[Daniele B]

@ilya.gorbunov thanks! it works

[ephemient]

there is a logically negated function as well:

myMap.keys.retainAll { it == myKeyValue }

[ephemient]

but if you want to remove everything in the map except for a single entry, consider something like

val value = myMap[myKeyValue]
myMap.clear()
if (value != null) myMap[myKeyValue] = value

which doesn't require an external iteration