why can t I do this ```val map = mutableMapOf lt Char Int gt

Question

why can t I do this ```val map = mutableMapOf lt Char Int gt map a += 1```

Russell Stewart · Answer

I think because there isn t an entry for `a` in the map yet If you re trying to add a value to it you would want ```map a = 1``` Or just set it in the definition ```val map = mutableMapOf lt Char Int gt a to 1 ```

oday · Answer

I want to construct the map based on characters from another String

Russell Stewart · Answer

However if you re trying to add 1 to whatever value is in the map then you d have to set that value first ```val map = mutableMapOf lt Char Int gt a to 1 map a += 1```

Russell Stewart · Answer

You mean assign each character in the string to a key in the map

Haris Khan · Answer

```+= is effective plusAssign``` plusAssign s receiver canot be null but map a is a nullable type

oday · Answer

```fun canConstruct ransomNote String magazine String Boolean val letters = mutableMapOf lt Char Int gt magazine forEach if it = letters it += 1 ```

oday · Answer

i want to have the characters in the magazine mapped out with 1 starting value for each character

Russell Stewart · Answer

OK then I think you just want to do ` = 1` instead of ` += 1`

oday · Answer

but later I will want to decrement that value

oday · Answer

and it definitely does exist as you saw I made a map out of each of the characters

oday · Answer

your example ```val map = mutableMapOf lt Char Int gt a to 1 map a += 1``` doesn t work same error

Russell Stewart · Answer

You made an empty map but I don t see where you re assigning values to it

Russell Stewart · Answer

If you want to assign the value `1` for each character then do ```magazine forEach if it = letters it = 1 ```

oday · Answer

I want to add 1

Russell Stewart · Answer

OK but you have to have a value to add it to At first there s nothing in there

oday · Answer

alright so I run that loop and after it i will be able to add

oday · Answer

```magazine forEach letters it += 1 ``` same error here

oday · Answer

that ran after the loop where i placed values inside

oday · Answer

the adding function itself expects null even if I don t have null in there

Russell Stewart · Answer

Yeah If you want the loop to add 1 if the values are already there you could try ```magazine forEach if it = if letters containsKey it letters it += 1 else letters it = 1 ```

oday · Answer

CONTAINSKEY

oday · Answer

ok that s the thing i missed

oday · Answer

thank you

Russell Stewart · Answer

No problem

oday · Answer

```map it = map it 0 + 1```

Russell Stewart · Answer

Yes that s much better Kind of embarrassed I didn t think of it slightly smiling face

oday · Answer

I just submitted the question and got to see other answers this was in one of them

Russell Stewart · Answer

Yeah this one is nice because it takes advantage of Kotlin s nullability features to make things more compact

nanodeath · Answer

if we re code golfing here s something else that you can try ```val foo = hello world val counts Map lt Char Int gt = foo groupingBy it eachCount ```