如何使用 LINQ 有条件地创建新的字符串数组？

Question

I have a string array like the following:

string[] myStrings = new string[] {"P1111111F","N1111110","Z2","P1111111F","Z1111110"};

How can I use LINQ to check each string is length = 8 and ends with "0" to get the following:

result: {"N","Y","N","N","Y"};

myStrings could be much longer with repeating strings so I'd like to achieve a solution that doesn't reprocess strings its already considered once.

Answer 1

The straightforward way:

string[] results = myStrings
    .Select(s => s?.Length == 8 && s.EndsWith("0") ? "Y" : "N")
    .ToArray();

The micro optimized way avoiding doubling algorithm of ToArray :

string[] results = new string[myStrings.Length];
for(int i = 0; i < myStrings.Length; i++)
{
    string s = myStrings[i];
    results[i] = s?.Length == 8 && s.EndsWith("0") ? "Y" : "N"; 
}

myStrings could be much longer with repeating strings so I'd like to achieve a solution that doesn't reprocess strings its already considered once.

I don't think that caching those results for example in a Dictionary<string, string> would help at all. The check if so easy and fast that any lookup would be less efficient. You'd just waste memory.