I am looking at the performance of a particular stock over a period of 30 days. I downloaded the data from Yahoo finance which appears as a CSV file. If I would like to create a new column in my dataset to show the daily percentage change between open and close using java refer to column H as where the output should appear, how should I do so?
Thanks in advance!
You can just edit your file line-by-line and add a separator character using the concat() function.
Open the file with a FileReader or BufferedReader and then start parsing.
Official Javadoc: https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#concat(java.lang.String)
Please see also this.
With OpenCSV: http://opencsv.sourceforge.net/
public class OpenCSVTest {
public static void main(String[] args) {
StringWriter target = new StringWriter();
try(CSVReader reader = new CSVReader(new StringReader("my,test"));
CSVWriter writer = new CSVWriter(target);) {
for(String[] line : reader) {
String[] added = Arrays.copyOf(line, line.length + 1);
added[added.length-1] = "addition";
writer.writeNext(added);
}
} catch (IOException e) {
e.printStackTrace();
}
System.out.println(target.toString());
}
}
You can replace the StringReader and StringWriter with your input and output. The reader will then iterate through each line in your csv for you. You can make a copy of the original line and add your new column and write it out into the target.
Breakdown of the code:
try(CSVReader reader = new CSVReader(new StringReader("my,test"));
CSVWriter writer = new CSVWriter(target);) { ... }
This is a try-with-resources block. It makes sure that the reader and writer are closed after they are done.
for(String[] line : reader) {
String[] added = Arrays.copyOf(line, line.length + 1);
added[added.length-1] = "addition";
writer.writeNext(added);
}
This is a standard for loop. The CSVReader implements the Iterable interface, which enables us to use it in the for loop directly.
Arrays.copyOf(line, line.length + 1); is a function that creates a copy of the array passed to it, but with a new size. Because you want to add a column, we make a copy of the original array my,test and add 1 more space at the end of it, where we can then assign the new value to it by doing: added[added.length-1] = "addition";
Finally, we just pass that to the writer which will then correctly write the values into the target, in this case a StringWriter, in your case likely a file.
