Kotlin : string to array to key value

Question

I'm trying to create a key => value Hashmap.

First, I have a string delimited by <br />. Then, I split it with split() (to get each string independently).

Then, I need to split each result with "=". The first part will be the key (I need it to be a string) and the second one will be the value (an int)

For now I have

val formules = objInput.getString(Constants.formules)
val hashmap = HashMap<String, Int>()
val resSplit = formules.split("<br />")
    resSplit.forEach {
      val splitFormule = it.split(" = ")
      val key = splitFormule.elementAt(0)
      val value = splitFormule.elementAt(1)
      Log.i(TAG, "$key")
}

I have this error when I'm trying to display the value :

Index: 1, Size: 1

At some point of time splitFormule contains only one element. Check it. — Sergio
– Sergio, Commented Dec 12, 2018 at 11:32
what did you expect? you may want to debug it and you will see the problem... could it be that your string doesn't contain any ` = `? — Roland
– Roland, Commented Dec 12, 2018 at 11:33
Yes @Rolan, it was that. It forgot to add this condition. Thanks, I feel kind of stupid ^^' — Projet Sin
– Projet Sin, Commented Dec 12, 2018 at 11:40

Patric · Accepted Answer · 2018-12-12 13:55:06Z

3

Be careful that your input is correct. Whitespaces are relevant. <br /> is different from <br/> and = is different from <space>=<space>. Assuming your input looks like this:

foo = 3<br />bar = 5<br />baz = 9000

Then you can create a map using this simple expression:

val map = formules
    .splitToSequence ("<br />") // returns sequence of strings: [foo = 3, bar = 5, baz = 9000]
    .map { it.split(" = ") } // returns list of lists: [[foo, 3 ], [bar, 5 ], [baz, 9000]]
    .map { it[0] to it[1] } // return list of pairs: [(foo, 3), (bar, 5), (baz, 9000)]
    .toMap() // creates a map from your pairs

edited Dec 12, 2018 at 13:55

answered Dec 12, 2018 at 13:11

Patric

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2 Comments

Roland Over a year ago

you may want to use splitToSequence instead of split otherwise you create a new list on each map-call, which you basically discard all when you call toMap...

Patric Over a year ago

Thank you very much @Roland! I was not aware of that. Made me read this interesting article about collections vs. sequences: blog.kotlin-academy.com/…

Roland · Accepted Answer · 2018-12-12 11:59:46Z

As you already said, you forgot a condition to check whether your string even contains a =.

Some furter notes: you can replace your elementAt also with get or with the indexing operator (e.g. splitFormule[0]).

You may also be interested in destructuring, e.g. your split could also be written as follows:

val (key, value) = it.split(" = ") // no need to extract the values from the array, if you know how the splitted data looks like
// you may even want to use the following if there could potentially be more than 1 '=' in the value part
val (key, value) = it.split(" = ", limit = 2) // at most 2 parts

Finally another variant, which skips keys if there aren't any values associated to them:

val yourMap = formules.splitToSequence("<br />")
    .filter { it.contains("=") }
    .map { it.split("""\s*=\s*""".toRegex(), limit = 2) }
    .map { (key, value) -> key to value } // destructuring
    .toMap()

// or: instead of filtering do a takeif and if you require those keys, do something appropriate there (e.g. set a default value instead)
val yourMap = formules.splitToSequence("<br />")
    .map { it.split("""\s*=\s*""".toRegex(), limit = 2) }
    .mapNotNull { it.takeIf { it.size == 2 } } // this discards now the entries without any value
    .map { (key, value) -> key to value } // destructuring
    .toMap()

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