从ArrayList访问索引值并将其存储在单独的新ArrayList中

Question

I currently have an ArrayList called months.

ArrayList<MonthData> months;

MonthData is a class that is basically a model for data.

public class MonthData {

  int y;
  int m;
  float h;
  ...


  public MonthData(String data) throws Exception {
    ...
    this.parseData(data);
  }


  void parseData(String csvData) {
    String[] parseResult = csvData.trim().split("\\s+");

    this.setYear(parseResult[0]);
    this.setMonth(parseResult[1]);
    ...


  public String toString() {
    return "y =" + year + ", m =" + month + ",...

  }


  public int getY() {
    return y;
  }

  // followed by lots of getters for: m, h, c, f, r, s, ... 

Now for the second public class...

public class Totals {
  private ArrayList<MonthData> months;


  public static void main(String args[]) throws IOException, Exception {
    Totals t = new Totals("..blah/../..blah/../Numbers.data");

  }

  public void readDataFile(String filename) throws IOException, Exception {
    FileReader file = new FileReader(filename);
    BufferedReader buffer = new BufferedReader(file);
    String line;

    buffer.readLine(); //skipping headers
    ...

    while (!(line = buffer.readLine()).isEmpty()) {
      this.months.add(new MonthData(line.trim()));
    }

    buffer.close();
    System.out.println(this.months);
  }

This class reads a file containing lots of data, here is a snippet of the data:

     y    m      h       c       f      r       s //here for your reference

   1930   1    8.1     2.4       6   120.5    54.2
   1930   2    4.4     0.6      12    22.2    29.1
   1930   3    8.1     2.1       9    76.2    88.2
    ...

When I System.out.println(this.months);

I get this:

y=1930, m=1, h=8.1, c=2.4, f=6, r=120.5, s=54.2, y =1930, m=2, h=4.4, c=0.6, f=12, r=22.2, s=29.1, ... etc.

As you can see it corresponds with the data file so I know the data is being read to the ArrayList months properly.

******** QUESTION *********** Now what I want to do is look at this ArrayList and get every r value and store them in a different ArrayList, lets say ArrayList rValues (so that i have an ArrayList full of r values only).

I know I need to iterate over this ArrayList somehow to the r value indexes, get the values and then store them in another ArrayList just dont know how!! :(

Any help here at all will be greatly appreciated. Happy to answer any questions, although i have possibly explained whats going on as best as i can. Thanks in advance guys :)

Answer 1

Why don't you iterate over list like this:

for (int i = 0; i<months.size(); i++)

and then you can get your MonthData object with this command

months.get(i)

and if you want just ar value then create getter for r ( getR() ) and call it and save in new array list:

Something like this:

ArrayList<Float> rValue = new ArrayList<>();
for (int i = 0; i<months.size(); i++)
{
    rValue.add(months.get(i).getR());
}

(thanks to @Mick Mnemonic) You can also use foreach loop

ArrayList<Float> rValue = new ArrayList<>();
for (MonthData m: months) 
{ 
    rValue.add(m.getR()); 
}