Speed up CSV reading code (vector of doubles)
As per Bobby's comment, Vector is your problem, but not for the reason he says...

Vector is a synchronized class. Each call to any method on Vector will lock the thread, flush all cache lines, and generally waste a lot of time (in a situation where it's usage is in a single thread only).

The fact that you use Vector indicates that you are running some really old code, or you have not properly read the JavaDoc for it.

A secondary performance problem is that each value is being converted to a Double Object. In cases where you have large amounts of data, and where there is a primitive available for you to use, it is always faster to use the primitive (in this case, double instead of Double).

You should also be using the Java7 try-with-resources mechanism for your stream.

My recommendation is to change the signature of your method to return a List... actually, no, my recommendation is to return an array of primitive double[].... if you are interested in speed, this will be a significant improvement:

private static double[] readTXTFileSingle(String csvFileName) throws IOException {
    double[] csvData = new double[4096]; // arbitrary starting size.
    int dcnt = 0;

    try (BufferedReader stream = new BufferedReader(new FileReader(csvFileName))) {
        String line = null;
        while ((line = stream.readLine()) != null) {
            String[] splitted = line.split(",");
            if( ! NumberUtils.isNumber(splitted[0])) {

                continue;
            }

            double dataLine = Double.parseDouble(splitted[0]);
            if (dcnt &gt;= csvData.length) {
                // add 50% to array size.
                csvData = Arrays.copyOf(csvData, dcnt + (dcnt / 2));
            }
            csvData[dcnt++] = dataLine;

        }
    }
    return Arrays.copyOf(csvData, dcnt);
}


Edit:

One other thing, if you want another tweak in performance, use:

String[] splitted = line.split(",", 2);


since you never access more than the first field in the record, you do not need to look for comma's beyond the first comma