How to sort list <List <String>>
I have a task to sort a text file with some requirements:
- sort rows by columns
- sort rows by 1st columns (if the data in the columns is the same, then by the 2nd column), etc. data in rows remains unchanged after sorting;
- numbers must be sorted in ascending order, and letters in alphabetical order - the number above the letter
- tab-delimited columns ("\ t")
what i did: read the file and copy everything to list> where each list item is a string from the file stored in the list, here is the code:
public class ReadDataFile {
public static List<List<String>> readData(String fileName) throws IOException {
BufferedReader br = new BufferedReader(new FileReader(fileName + ".txt"));
List<List<String>> data = new ArrayList<List<String>>();
String line;
while (true) {
line = br.readLine();
if (line == null)
break;
List<String>lines = Arrays.asList(line.split("\t"));
data.add(lines);
System.out.println(lines);
}
br.close();
return data;
and writes the data to another file:
public void writeToFile(String fileName) throws IOException {
FileWriter writer = new FileWriter(fileName);
List<List<String>> data = ReadDataFile.readData("input");
Collections.sort(data, new Comparator<List<String>>() {
@Override
public int compare(List<String> o1, List<String> o2) {
// TODO Auto-generated method stub
return o1.get(0).compareTo(o2.get(0));
}
});
for (List<String> lines : data) {
for (int i = 0; i < lines.size(); i++) {
writer.write(lines.get(i));
if (i < lines.size() - 1) {
writer.write("\t");
}
}
writer.write("\n");
}
writer.close();
}
the problem is that:
public int compare(List<String> o1, List<String> o2) {
// TODO Auto-generated method stub
return o1.get(0).compareTo(o2.get(0));
}
doesn't sort correctly what I need.
there is an example of an input file:
-2.2 2 3 4 329 2
2.2 12345q 69 -afg
2.2 12345q 69 -asdf
-22 1234234 asdfasf asdgas
-22 11 abc
-22 -3 4
-1.1
qqqq 1.1
Final expected result:
-22 -3 4
-22 11 abc
-22 1234234 asdfasf asdgas
-2.2 2 3 4 329 2
-1.1
2.2 12345q 69 -afg
2.2 12345q 69 -asdf
qqqq 1.1
but i get:
-1.1
-2.2 2 3 4 329 2
-22 -3 4
-22 11 abc
-22 1234234 asdfasf asdgas
2.2 12345q 69 -afg
2.2 12345q 69 -asdf
qqqq 1.1
The question is, how do you write the correct view? thanks for answers
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It sounds like you need string values that are valid numbers to sort using number comparison. Since your example contains non-integer values, you can compare numbers using double
or BigDecimal
. The code below uses BigDecimal
so numbers of any size can be compared without loss of precision, but does not support special values for "Infinite"
, "-Infinite"
and "NaN"
, or a format HexFloatingPointLiteral
that does Double.parseDouble()
.
Comparing a number to a string must sort the number before the string.
For string-to-string comparisons, you can sort lexicographically , case-insensitively, or use Collator
for locale-sensitive comparisons. Below code uses Collator for default locale.
Comparison compares the first value of the list, and if equal will compare the second value, etc. If one list is shorter and the lists are equal up to that point, the shorter list is sorted first.
public final class NumberStringComparator implements Comparator<List<String>> {
private Collator collator = Collator.getInstance();
@Override
public int compare(List<String> r1, List<String> r2) {
for (int i = 0; ; i++) {
if (i == r1.size())
return (i == r2.size() ? 0 : -1);
if (i == r2.size())
return 1;
String v1 = r1.get(i), v2 = r2.get(i);
BigDecimal n1 = null, n2 = null;
try { n1 = new BigDecimal(v1); } catch (@SuppressWarnings("unused") NumberFormatException unused) {/**/}
try { n2 = new BigDecimal(v2); } catch (@SuppressWarnings("unused") NumberFormatException unused) {/**/}
int cmp = (n1 == null ? (n2 == null ? this.collator.compare(v1, v2) : 1) : (n2 == null ? -1 : n1.compareTo(n2)));
if (cmp != 0)
return cmp;
}
}
}
Test
String input = "-2.2\t2\t3\t4\t329\t2\n" +
"2.2\t12345q\t69\t-afg\n" +
"2.2\t12345q\t69\t-asdf\n" +
"-22\t1234234\tasdfasf\tasdgas\n" +
"-22\t11\tabc\n" +
"-22\t-3\t4\n" +
"-1.1\n" +
"qqqq\t1.1";
List<List<String>> data = new ArrayList<>();
try (BufferedReader in = new BufferedReader(new StringReader(input))) {
for (String line; (line = in.readLine()) != null; )
data.add(Arrays.asList(line.split("\t")));
}
data.sort(new NumberStringComparator());
data.forEach(System.out::println);
Output
[-22, -3, 4] [-22, 11, abc] [-22, 1234234, asdfasf, asdgas] [-2.2, 2, 3, 4, 329, 2] [-1.1] [2.2, 12345q, 69, -afg] [2.2, 12345q, 69, -asdf] [qqqq, 1.1]
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