C＃LINQ：字符串（“[1,2,3]”）如何解析为数组？

Question

I am trying to parse a string into array and find a very concise approach.

string line = "[1, 2, 3]";
string[] input = line.Substring(1, line.Length - 2).Split();
int[] num = input.Skip(2)
                 .Select(y => int.Parse(y))
                 .ToArray();

I tried remove Skip(2) and I cannot get the array because of non-int string. My question is that what is the execution order of those LINQ function. How many times is Skip called here?

Thanks in advance.

Answer 1

The order is the order that you specify. So input.Skip(2) skips the first two strings in the array, so only the last remains which is 3 . That can be parsed to an int . If you remove the Skip(2) you are trying to parse all of them. That doesn't work because the commas are still there. You have splitted by white-spaces but not removed the commas.

You could use line.Trim('[', ']').Split(','); and int.TryParse :

string line = "[1, 2, 3]";
string[] input = line.Trim('[', ']').Split(',');
int i = 0;
int[] num = input.Where(s => int.TryParse(s, out i)) // you could use s.Trim but the spaces don't hurt
                 .Select(s => i)
                 .ToArray(); 

Just to clarify, i have used int.TryParse only to make sure that you don't get an exception if the input contains invalid data. It doesn't fix anything. It would also work with int.Parse .

Update : as has been proved by Eric Lippert in the comment section using int.TryParse in a LINQ query can be harmful. So it's better to use a helper method that encapsulates int.TryParse and returns a Nullable<int> . So an extension like this:

public static int? TryGetInt32(this string item)
{
    int i;
    bool success = int.TryParse(item, out i);
    return success ? (int?)i : (int?)null;
}

Now you can use it in a LINQ query in this way:

string line = "[1, 2, 3]";
string[] input = line.Trim('[', ']').Split(',');
int[] num = input.Select(s => s.TryGetInt32())
                 .Where(n => n.HasValue)
                 .Select(n=> n.Value)
                 .ToArray();

Answer 2

The reason it does not work unless you skip the first two lines is that these lines have commas after int s. Your input looks like this:

"1," "2," "3"

Only the last entry can be parsed as an int ; the initial two will produce an exception.

Passing comma and space as separators to Split will fix the problem:

string[] input = line
    .Substring(1, line.Length - 2)
    .Split(new[] {',', ' '}, StringSplitOptions.RemoveEmptyEntries);

Note the use of StringSplitOptions.RemoveEmptyEntries to remove empty strings caused by both comma and space being used between entries.

Answer 3

我觉得你这样做会更好：

JsonConvert.DeserializeObject(line, typeof(List<int>));

Answer 4

you might try

    string line = "[1,2,3]";
    IEnumerable<int> intValues = from i in line.Split(',')
                                 select Convert.ToInt32(i.Trim('[', ' ', ']'));