Parse .txt directly into Arraylist

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chris.kra..

Parse .txt directly into Arraylist

in Programming Questions • 1 year ago

I am parsing some numerical values from a .txt file to an arraylist. Right now i'm doing that like this:

// create arraylist
ArrayList values = new ArrayList();
// load values into temporary int array
int[] v = int(loadStrings("values.txt"));
// copy contents of temporary int array to arraylist
for (int i=0; i<v.length; i++) {
values.add(v[i]);
}
println(values.size());

As you can see i'm not parsing directly into the arraylist, but with an intermediate int[] (because i don't know how many lines the txt-file has). I would like to skip this step, but have not been able to figure out how. Does anyone know how to parse directly into the arraylist?

Replies(4)

maleo

Re: Parse .txt directly into Arraylist

1 year ago

you can use a buffered reader to feed one line at a time into the arraylist. i also converted the strings to integers in the example like you did in your code. each value needs to be on a separate line in the txt file.

ArrayList values = new ArrayList();
String line;
BufferedReader reader = createReader("values.txt");
try {
while((line = reader.readLine()) != null) {
values.add(int(line));
}
} catch (IOException e) {
e.printStackTrace();
}
println(values);

chris.kra..

Re: Re: Parse .txt directly into Arraylist

1 year ago

Thanks! Btw. i changed your String variable name, as line is already a native function in Processing, so just as a precaution.

PhiLho

Re: Parse .txt directly into Arraylist

1 year ago

Why do you want to avoid the extra step?
Do you plan to add more values into values?
If not, the best way is just to avoid using the ArrayList, which is eating much more memory than the v array anyway.
If you need to grow the list, your way is fine, unless perhaps you read a file being several megabytes in size. In this case, the way shown by maleo is fine.
A little optimization of your way: initialize the array list with the length of v:
ArrayList values; // Global declaration (if needed)
[...]
values = new ArrayList(v.lenght);
for ( ... )

It will be more efficient as not having to grow the internal array of values (implying a copy of the old array in this case).

chris.kra..

Re: Re: Parse .txt directly into Arraylist

1 year ago

Yeah, but I made it an arraylist because i'm removing values from it, otherwise i would've used your suggestion (regular int array).

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