Android array of arrays with string as index

Question

I'm looking for something that is surely very simple, but I don't know the best way to do it.

I could have 2 arrays of strings (that I don't know size at start), containing something like:

down[0]:"file1"
down[1]:"file2"
...
up[0]:"file3"
up[1]:"file4"
...

But I'd like them in the same array like:

array["down"][0]:"file1"
array["down"][1]:"file2"
array["up"][0]:"file3"
array["up"][1]:"file4"

And insert data with:

array[mykey].put(filename);

And loop through the data with:

for (String st : array["down"])
...
for (String st : array["up"])
...

Thanks for your ideas.

Hmm. I never saw array indexed with string. As I know, this is not possible. If I am wrong correct me. If you want to do such a thing you should make a method where output is int and looks like array[yourMethod("down")]. Just try to find "down" in an array and make index as an output — Apuna12
– Apuna12, Commented Dec 4, 2018 at 19:35

Kevin Coppock · Accepted Answer · 2018-12-04 22:32:50Z

1

It sounds like you want a MutableMap<String, MutableList<String>>. In Kotlin, for example:

val data = mutableMapOf(
  "down" to mutableListOf("file1", "file2"),
  "up" to mutableListOf("file3", "file4")
)

Then you can access like:

data["down"].forEach { file ->
  // do something with file
}

Or mutate it like:

data["down"].add("file5")

For Java, you'll have to be a bit more verbose, but you can accomplish a similar result:

Map<String, List<String>> data = new HashMap<>();

List<String> downList = new ArrayList<>();
downList.add("file1");
downList.add("file2");
data.put("down", downList);

List<String> upList = new ArrayList<>();
upList.add("file3");
upList.add("file4");
data.put("up", upList);

Then:

for (String file : data.get("down")) {
  // do something with file
}

Or mutate it like:

data.get("down").add("file5");

edited Dec 4, 2018 at 22:32

answered Dec 4, 2018 at 19:34

Kevin Coppock

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2 Comments

François De La Rosnie Over a year ago

Sorry, I don't use Kotlin.

Kevin Coppock Over a year ago

Ah okay, I wasn't sure from the tags. I've updated to include a Java answer too. Same data structures apply, it's just more verbose.

Mark Gilchrist · Accepted Answer · 2018-12-04 20:27:17Z

0

if you are using Kotlin you could do

val data : MutableMap<String,MutableList<String>> = mutableMapOf()
data["up"] = mutableListOf()
data["down"] = mutableListOf()

// add file to up
data["up"]?.add("file1")

// get the first up
val firstUp = data["up"]?.get(0)

// map over all the ups if the are there
data["up"]?.forEach { str ->

    }

edited Dec 4, 2018 at 20:27

answered Dec 4, 2018 at 19:48

Mark Gilchrist

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