Convert 2D array to string in C#, looking for most elegant way

Question

I cannot believe there is no smart way to get something like this from a 2D array,
in this case int[,] a:

"{1,2,3},{4,5,6},{7,8,9}"

I have read many similar questions and learned that string.Join() can only be used on jagged arrays (in 2D). But I don't want to use them because of the more complex initialization and because it just feels bad when my rows, which all have the same length, are spread over several places in memory.

This is my "normal" code:

var s = "";
for (int i = 0; i < a.GetLength(0); i++) {
    if (i > 0) s += ',';
    s += '{';
    for (int j = 0; j < a.GetLength(1); j++) {
        if (j > 0) s += ',';
        s += a[i, j];
    }
    s += '}';
}

And here a "golfed" one:

var s = "{";
var i = 0;
foreach (var item in a) s += (i++ > 0 ? i % a.GetLength(1) == 1 ? "},{" : "," : "") + item;
s += '}';

:) - not really elegant, too, and the readability is more than bad.

Any suggestions? I'm open to Linq, since it doesn't have to be fast. I'm interested in improving elegance of the code, but not by just moving it to an extension method.

shA.t · Accepted Answer · 2017-10-10 08:51:41Z

AFAIK, when we want a string from an object, we are calling about serializing, So I prefer to use a serializer like Newtonsoft.Json:

var result = $@"{{{JsonConvert.SerializeObject(a)
    .Trim('[', ']').Replace("[", "{").Replace("]", "}")}}}";

A way by using simple fors like your solution and with removing ifs can be - this code will be faster for small arrays -:

var result = string.Empty;
var maxI = a.GetLength(0);
var maxJ = a.GetLength(1);
for (var i = 0; i < maxI; i++)
{
    result += ",{";
    for (var j = 0; j < maxJ; j++)
    {
        result += $"{a[i, j]},";
    }

    result += "}";
}

result = .Replace(",}", "}").Substring(1);

As suggested to use StringBuilder to improve performance just for big arrays:

var sb = new StringBuilder(string.Empty);
var maxI = a.GetLength(0);
var maxJ = a.GetLength(1);
for (var i = 0; i < maxI; i++)
{
    sb.Append(",{");
    for (var j = 0; j < maxJ; j++)
    {
        sb.Append($"{a[i, j]},");
    }

    sb.Append("}");
}

sb.Replace(",}", "}").Remove(0, 1);
var result = sb.ToString();

M.kazem Akhgary · Accepted Answer · 2017-10-08 17:30:33Z

Linq solution, not performance wise.

var str = string.Join(",", a.OfType<int>()
    .Select((value, index) => new {value, index})
    .GroupBy(x => x.index / a.GetLength(1))
    .Select(x => $"{{{string.Join(",", x.Select(y => y.value))}}}"));

Note that you cant Select on 2d array, but you can use OfType which will return an enumerable for 2d array, the enumerator will traverse through 2d array horizontally.

x.index / a.GetLength(1) simply divides each index to total number of rows. so if you have 3 rows, your indexes will be distributed through 3 rows equivalently.

lastly string join is operated on each group.

A little more simplified version. (format inside result selector of grouping)

var str = string.Join(",", a.OfType<int>()
    .Select((value, index) => new {value, index})
    .GroupBy(x => x.index / a.GetLength(1), x => x.value,
        (i, ints) => $"{{{string.Join(",", ints)}}}"));

mjwills · Accepted Answer · 2017-10-08 11:42:36Z

1

Consider this approach:

var numbers = new int[,] { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };

var results = string.Join(",",
    Enumerable.Range(0, numbers.GetUpperBound(0) + 1)
        .Select(x => Enumerable.Range(0, numbers.GetUpperBound(1) + 1)
            .Select(y => numbers[x, y]))
        .Select(z => "{" + string.Join(",", z) + "}"));

Console.WriteLine(results);

Console.ReadLine();

It is quite similar to yours, but using LINQ instead. It projects the two dimensional array into a LINQ enumerable, and then wraps it with braces and adds commas where needed.

answered Oct 8, 2017 at 11:42

mjwills

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Comments

Shimmy Weitzhandler · Accepted Answer · 2019-11-18 10:35:25Z

-1

Posting this answer just for the reference, for when you don't mind the data to be presented in a continuous manner and when the bounds are static and always known.

You can just output your string as plain csv, using LINQ Cast, then string.Join.

var array = new int[2,3] { { 1, 2, 3 }, { 1, 2, 3 } };
var output = string.Join(',', array.Cast<int>());

To parse it back:

var input = new int[upperLen,lowerLen];
for (var upper = 0; upper < upperLen; upper++)
    for(var lower = 0; lower < lowerLen; lower++)
        input[upper, lower] = int.Parse(parsed[(upper * lowerLen) + lower]);

See example here.

edited Nov 18, 2019 at 10:35

answered Nov 16, 2019 at 20:18

Shimmy Weitzhandler

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1 Comment

maf-soft Over a year ago

This does not meet the requirements or you have interpreted them too generously. It wasn't about being able to parse it back, it was about presenting the data in a structured way.

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