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POAny way to improve this string slice method?
 

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  1. POAny way to improve this string slice method?
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    <p>I wrote this string extension awhile back, and I'm actually getting quite a bit of use out of it.</p> <pre><code>public static string Slice(this string str, int? start = null, int? end = null, int step = 1) { if (step == 0) throw new ArgumentException("Step cannot be zero.", "step"); if (start == null) { if (step &gt; 0) start = 0; else start = str.Length - 1; } else if (start &lt; 0) { if (start &lt; -str.Length) start = 0; else start += str.Length; } else if (start &gt; str.Length) start = str.Length; if (end == null) { if (step &gt; 0) end = str.Length; else end = -1; } else if (end &lt; 0) { if (end &lt; -str.Length) end = 0; else end += str.Length; } else if (end &gt; str.Length) end = str.Length; if (start == end || start &lt; end &amp;&amp; step &lt; 0 || start &gt; end &amp;&amp; step &gt; 0) return ""; if (start &lt; end &amp;&amp; step == 1) return str.Substring((int)start, (int)(end - start)); int length = (int)(((end - start) / (float)step) + 0.5f); var sb = new StringBuilder(length); for (int i = (int)start, j = 0; j &lt; length; i += step, ++j) sb.Append(str[i]); return sb.ToString(); } </code></pre> <p>Since it's in all my projects now, I'm wondering if I could have done it better. More efficient, or would it produce unexpected results in any case?</p> <hr> <p>Slice. It works like Python's array notation.</p> <pre><code> "string"[start:end:step] </code></pre> <p>Many other languages have something like this too. <code>string.Slice(1)</code> is equivalent to <code>string.Substring(1)</code>. <code>string.Substring(1,-1)</code> trims off the first and last character. <code>string.Substring(null,null,-1)</code> will reverse the string. <code>string.Substring(step:2)</code> will return a string with every other character... also similar to <a href="http://www.w3schools.com/jsref/jsref_slice_array.asp" rel="nofollow">JS's slice</a> but with an extra arg.</p> <hr> <p>Re-revised based on your suggestions:</p> <pre><code>public static string Slice(this string str, int? start = null, int? end = null, int step = 1) { if (step == 0) throw new ArgumentException("Step size cannot be zero.", "step"); if (start == null) start = step &gt; 0 ? 0 : str.Length - 1; else if (start &lt; 0) start = start &lt; -str.Length ? 0 : str.Length + start; else if (start &gt; str.Length) start = str.Length; if (end == null) end = step &gt; 0 ? str.Length : -1; else if (end &lt; 0) end = end &lt; -str.Length ? 0 : str.Length + end; else if (end &gt; str.Length) end = str.Length; if (start == end || start &lt; end &amp;&amp; step &lt; 0 || start &gt; end &amp;&amp; step &gt; 0) return ""; if (start &lt; end &amp;&amp; step == 1) return str.Substring(start.Value, end.Value - start.Value); var sb = new StringBuilder((int)Math.Ceiling((end - start).Value / (float)step)); for (int i = start.Value; step &gt; 0 &amp;&amp; i &lt; end || step &lt; 0 &amp;&amp; i &gt; end; i += step) sb.Append(str[i]); return sb.ToString(); } </code></pre>
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    1. COWhat's it supposed to do? I know I could work it out, but I'm feeling a bit lazy...
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    2. COis that substring!?
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    3. COI'm intrigued as to know what you use it for? The step bit is intriguing. I understand what it does, but what is the practical application. Just interested.
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