Java - How to split a string which is column based?

Question

I have following 2 rows in a file:

16.1 14.3 8.8 7.0 7.85 13.29 18.75 13.08 13.10

6.7 5.4 6.39

I am able to split 1st row by using "\\s+" regex. But I cannot split 2nd row. I want to split above strings in such a way that I will get following output:

row[1] = [16.1, 14.3, 8.8, 7.0, 7.85, 13.29, 18.75, 13.08, 13.10]
row[2] = [6.7, 5.4, null, null, 6.39, null, null, null, null]

Below is the screenshot of what I have to parse :

Not sure that edit just now was a good idea because it definitely changed the formatting of the input. It now has a defined number of whitespaces as before it did not have. Could the original poster please confirm whether the number of whitespaces between your entries follows some definition? — Ben, Mar 15 '18 at 12:30
Maybe to further elaborate, how would the file look if we replace the `18.75` in the first row with a `23132.3312`? Is that even possible? To say it simple: When there is no definition how your file is going to look like there isn't a way to parse it. — Ben, Mar 15 '18 at 12:33
What is the maximum length of single number? If it can grow to more than distance between two numbers, you won't be able to use regular expressions for the split. — vasek, Mar 15 '18 at 12:35
@Ben, That edit was not a good idea because my original answer don't have specific number of spaces. I will re-edit it. — Pranit More, Mar 15 '18 at 12:35
Okay. Maybe also add what definitions there are. Is the number of columns fixed? The spacing? The size of the numbers? Encoding? Stuff like this would be helpful to find some way to parse this. — Ben, Mar 15 '18 at 12:37
That screenshot doesn't contain "empty" values. Anyway it looks like we can assume that columns contain some fixed amount of characters (including spaces). But is it same amount of characters for each column? — Pshemo, Mar 15 '18 at 12:40
@saifahmad, No data is not `TAB` spaced. Please look for @YCF_L's solution. It is the correct solution. — Pranit More, Mar 15 '18 at 13:02
@saifahmad, At first I didn't recognize that all the columns have specific length of characters, i.e. 7. That's why YCF_L's solution is correct. — Pranit More, Mar 15 '18 at 14:25

Youcef LAIDANI · Accepted Answer · 2018-03-15T13:23:11.730

2

It seems that your inputs has a fixed length (7) between the start of the first number to the next start number :

16.1   14.3    8.8    7.0    7.85  13.29  18.75  13.08   13.10
^^^^^^^--------(7)

In this case you can split your input using this regex (?<=\\G.{7}) take a look at this :

String text1 = "16.1   14.3    8.8    7.0    7.85  13.29  18.75  13.08   13.10";
String text2 = "6.7    5.4                   6.39                             ";

String[] split1 = text1.split("(?<=\\G.{7})");
String[] split2 = text2.split("(?<=\\G.{7})");

Outputs

[16.1   , 14.3   ,  8.8   ,  7.0   ,  7.85  , 13.29  , 18.75  , 13.08  ,  13.10]
[6.7    , 5.4    ,        ,        ,  6.39  ,        ,        ,        ,       ]

Better Solution

If you want to get null instead of empty you can use :

List<String> result = Arrays.asList(text2.split("(?<=\\G.{7})"))
        .stream()
        .map(input -> input.matches("\\s*") ? null : input.trim())
        .collect(toList());

Outputs

[16.1, 14.3, 8.8, 7.0, 7.85, 13.29, 18.75, 13.08, 13.10]
[6.7, 5.4, null, null, 6.39, null, null, null, null]

edited Mar 15 '18 at 13:23

answered Mar 15 '18 at 12:44

Youcef LAIDANI

55,661
15
90
140

Are you sure `text2` from OP has those trailing spaces? – revo Mar 15 '18 at 12:46
@revo, Yes, It has trailing spaces. – Pranit More Mar 15 '18 at 12:49
@PranitMore you have to mention that in your question please, the comment of revo is a good point – Youcef LAIDANI Mar 15 '18 at 12:51
Thanks YCF_L! This solution works. Thanks a lot! Sorry it was my mistake. I should have mentioned about trailing spaces before. And can you please explain this regex `(?<=\\G.{7})` ? – Pranit More Mar 15 '18 at 12:58
4

@PranitMore it is a trick to split a String in a specific length to understand more take a look at this answer here https://stackoverflow.com/a/3761521/5558072 – Youcef LAIDANI Mar 15 '18 at 13:04

ernest_k · Answer 2 · 2018-03-15T12:47:18.813

0

You can use streams and split rows then cells, resulting in a list of lists:

List<List<String>> matrix = Arrays.asList(text.split("\n"))
            .stream()
            .map(line -> Arrays.asList(line.split("\\s+")))
            .collect(Collectors.toList())

This gives you a 2D array/list of the values.

When tested with:

String text = "16.1   14.3    8.8    7.0    7.85  13.29  18.75  13.08   13.10\n" + " 6.7    5.4                   6.39";

That outputs:

[[16.1, 14.3, 8.8, 7.0, 7.85, 13.29, 18.75, 13.08, 13.10], [, 6.7, 5.4, 6.39]]

edited Mar 15 '18 at 12:47

answered Mar 15 '18 at 12:42

ernest_k

44,416
5
53
99

This solution doesn't satisfy my criteria, as I need empty columns as well in the solution. – Pranit More Mar 15 '18 at 13:00

score 0 · Answer 3 · answered Mar 15 '18 at 13:01

Use Guava's `Splitter.fixedLength(int)`

String[] rows = {
    "16.1   14.3    8.8    7.0    7.85  13.29  18.75  13.08   13.10",
    "6.7    5.4                   6.39                             "
  };
Splitter splitter = Splitter.fixedLength(7);
for(String row: rows) {
  List<String> data = splitter.splitToList(row);
  for (int i = 0; i < data.size(); i++) {
    System.out.printf("Column %d: %s%n", i+1, data.get(i));
  }
}

score -1 · Answer 4 · answered Mar 15 '18 at 12:37

-1

TO me this seems like a fixed width file .

Please try following regex

.{7}

You can change value within curly braces depending on width of column,

.{column_width_goes_here}

Sample https://regex101.com/r/SZZxbB/1

answered Mar 15 '18 at 12:37

Vaibhav Patil

132
1
6

Java - How to split a string which is column based?

4 Answers4

Better Solution

Use Guava's Splitter.fixedLength(int)

Use Guava's `Splitter.fixedLength(int)`