How to convert ArrayList<String> to Float[]

Question

I have to retrieve some data from a file to show it in a chart. The function that shows the chart requires he data as float[] whereas the retrieved data is in the form ArrayList<String>.

What is the easiest way to convert ArrayList<String> to float[]?

        try {
            FileInputStream fIn = context.openFileInput(fileDir+fileName);
            InputStreamReader ipsr = new InputStreamReader(fIn);
            BufferedReader b = new BufferedReader(ipsr);

            ArrayList<String> list_prix = new ArrayList<String>();
            String ligne;

            while ((ligne = b.readLine()) != null) {
                String dtVal = ligne.split(" ")[2];
                dtVal = dtVal.substring(0, dtVal.length() - 2);
                list_prix.add(dtVal);
            }

            //just here if i can convert list_prix to float[]

            fIn.close();
            ipsr.close();
        } 
        catch (Exception e) 
        {
            Log.e("blah", "Exception", e);
        }

Thank you for your help.

What have you tried?

Charles Goodwin
– Charles Goodwin

2011-09-11 16:42:53 +00:00
Commented Sep 11, 2011 at 16:42 — Charles Goodwin
– Charles Goodwin, Commented Sep 11, 2011 at 16:42
@Charles Goodwin: Please see my edited post.

androniennn
– androniennn

2011-09-11 16:45:35 +00:00
Commented Sep 11, 2011 at 16:45 — androniennn
– androniennn, Commented Sep 11, 2011 at 16:45
do you need list_prix after the while loop

confucius
– confucius

2011-09-11 16:47:28 +00:00
Commented Sep 11, 2011 at 16:47 — confucius
– confucius, Commented Sep 11, 2011 at 16:47
@Nammari:Yes,exactly. After the while->loop.

androniennn
– androniennn

2011-09-11 16:49:29 +00:00
Commented Sep 11, 2011 at 16:49 — androniennn
– androniennn, Commented Sep 11, 2011 at 16:49

Andrew White · Accepted Answer · 2011-09-11 16:48:39Z

3

I think the following will do it using Guava...

Collection<Float> floats = Collections2.transform(list_prix, new Function<String, Float>() {
    public Float apply(String input) {
        return Float.parseFloat(input);
    }

});

Float[] floatArray = new Float[floats.size()];
floats.toArray(floatArray);

answered Sep 11, 2011 at 16:48

Andrew White

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2 Comments

Cristian Over a year ago

IMHO, installing Guava just for that would be like killing a fly with a nuclear bomb.

Charles Goodwin Over a year ago

Agree with @Cristian but I voted it up as an interesting alternative :-)

Charles Goodwin · Accepted Answer · 2011-09-12 00:27:56Z

2

You can loop and use Float.parseFloat().

float [] floatValues = new float[list_prix.size()];

for (int i = 0; i < list_prix.size(); i++) {
    floatValues[i] = Float.parseFloat(list_prix.get(i));
}

Now, this assumes that every string in your ArrayList can actually be parsed into a float. If not, it could throw an exception, so you may want to do this in a try/catch block if you are not sure.

edited Sep 12, 2011 at 0:27

Charles Goodwin

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answered Sep 11, 2011 at 16:46

Richard

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5 Comments

Charles Goodwin Over a year ago

I would classify this answer as "hand holding" but nevermind.

androniennn Over a year ago

And please how to convert arraylist<string> to string[]. Looking for your response please. I've tried to change the above code to change it to String but have always an error.

androniennn Over a year ago

for (int i = 0; i < list_date.size(); i++) { list_date.toArray(dateValues);

Richard Over a year ago

Well, the string version would look pretty similar: stringValues[i] = list_prix.get(i); This works since list_prix is an arraylist of strings (defined by ArrayList<String>)

Richard Over a year ago

@Charles Goodwin: I guess it is a bit of hand holding, but we've all been there before. A post like this might help other newbies that may not know about "parseFloat", "parseInt", etc.

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