wan2land · August 29, 2015 14:02 · Jun 10, 2014 · Nov 24, 2013 · Sep 3, 2013 · Sep 3, 2013
diff --git a/gistfile1.js b/gistfile1.js
@@ -1,3 +1,5 @@
+//참고 : http://jsperf.com/count-the-number-of-characters-in-a-string
+
 //www.lsauer.com 2012
 //Answer to:
 //http://stackoverflow.com/questions/881085/count-the-number-of-occurances-of-a-character-in-a-string-in-javascript/10671743#10671743

diff --git a/gistfile1.js b/gistfile1.js
@@ -16,7 +16,7 @@
 #3.
     var stringsearch = "o"
        ,str = "this is foo bar";
-    for(var count=-1,index=0; index != -1; count++,index=str.indexOf(stringsearch,index+1) );
+    for(var count=-1,index=-2; index != -1; count++,index=str.indexOf(stringsearch,index+1) );
      //>count:2
 #4.
 //searching for a single character
@@ -83,4 +83,8 @@ var str   = "this is foo bar",
          hist[str[si]] = hist[str[si]] ? 1+hist[str[si]]:1;
     }
     //>hist[schar]
-    2
+    2
+
+//Changelog > 11/2013:
+//
+// 24/11/2013   #3 bug fixed in initial index position; pointed out by Augustus@Stackoverflow
diff --git a/gistfile1.js b/gistfile1.js
@@ -46,7 +46,9 @@
 #7
 //based on typed arrays; str2buffer is taken from 'is-lib'; See: https://gist.github.com/lsauer
     //Converts an ASCII string to an typed-Array buffer
-    str2buffer = function(s){ var bu = new ArrayBuffer(s.length), aUint8 = new Uint8Array(bu ); for(var i=0; i<bu.byteLength; aUint8[i]=s.charCodeAt(i),i++);return aUint8 ;};
+    str2buffer = function(s){ var bu = new ArrayBuffer(s.length), aUint8 = new Uint8Array(bu );
+                              for(var i=0; i<bu.byteLength; aUint8[i]=s.charCodeAt(i),i++);return aUint8;
+    };
     var bstr = str2buffer ("this is foo bar")
        ,schar = 'o'.charCodeAt()
        ,cnt=0;

diff --git a/gistfile1.js b/gistfile1.js
@@ -68,5 +68,17 @@
 //see: http://stackoverflow.com/questions/10293378/what-is-the-most-efficient-way-of-merging-1-2-and-7-8-into-1-7-2-8/17910641#17910641
 var str   = "this is foo bar",
     schar = 'o'; 
-str.split('').reduce( function(p,c,i,a){ if(c === schar || p === schar){return isNaN(parseInt(p))? 1:+p+1;} return p;} ) 
+    str.split('').reduce( 
+        function(p,c,i,a){ if(c === schar || p === schar){return isNaN(parseInt(p))? 1:+p+1;} return p;}
+    ) 
 //Note: faster: c === schar || p === schar; slower: (c+p).indexOf(schar)>-1
+
+#10. dictionary character histogram
+var str   = "this is foo bar",
+    schar = 'o',
+    hist={}; 
+    for(si in str){
+         hist[str[si]] = hist[str[si]] ? 1+hist[str[si]]:1;
+    }
+    //>hist[schar]
+    2
diff --git a/gistfile1.js b/gistfile1.js
@@ -62,3 +62,11 @@
     for(var i=0;i<ubstr.length;schar!==ubstr[i++]||cnt++);
     //>cnt
     2
+
+#9
+//using reduce. Note: Element map functions are powerful but slow as they involve their own heap/stack allocation
+//see: http://stackoverflow.com/questions/10293378/what-is-the-most-efficient-way-of-merging-1-2-and-7-8-into-1-7-2-8/17910641#17910641
+var str   = "this is foo bar",
+    schar = 'o'; 
+str.split('').reduce( function(p,c,i,a){ if(c === schar || p === schar){return isNaN(parseInt(p))? 1:+p+1;} return p;} ) 
+//Note: faster: c === schar || p === schar; slower: (c+p).indexOf(schar)>-1
diff --git a/gistfile1.js b/gistfile1.js
@@ -52,4 +52,13 @@
        ,cnt=0;
     for(var i=0;i<bstr.byteLength;schar!==bstr[i++]||cnt++);
     //>cnt
-    2
+    2
+#8
+//based on untyped Arrays. Is expected to be slower. Analogous to #7
+    var ubstr = "this is foo bar".split('').map( function(e,i){ return e.charCodeAt();} )
+       //>[116, 104, 105, 115, 32, 105, 115, 32, 102, 111, 111, 32, 98, 97, 114]
+       ,schar = 'o'.charCodeAt()
+       ,cnt=0;
+    for(var i=0;i<ubstr.length;schar!==ubstr[i++]||cnt++);
+    //>cnt
+    2
diff --git a/gistfile1.js b/gistfile1.js
@@ -42,3 +42,14 @@
     var str = "this is foo bar";
     str.length - str.replace(/o/g,'').length
     //>2
+
+#7
+//based on typed arrays; str2buffer is taken from 'is-lib'; See: https://gist.github.com/lsauer
+    //Converts an ASCII string to an typed-Array buffer
+    str2buffer = function(s){ var bu = new ArrayBuffer(s.length), aUint8 = new Uint8Array(bu ); for(var i=0; i<bu.byteLength; aUint8[i]=s.charCodeAt(i),i++);return aUint8 ;};
+    var bstr = str2buffer ("this is foo bar")
+       ,schar = 'o'.charCodeAt()
+       ,cnt=0;
+    for(var i=0;i<bstr.byteLength;schar!==bstr[i++]||cnt++);
+    //>cnt
+    2
diff --git a/gistfile1.js b/gistfile1.js
@@ -35,4 +35,10 @@
              .filter(Boolean)
     //>[9, 10]
     [9, 10].length
-    //>2
+    //>2
+
+#6
+//'deleting' the character out of the string and measuring the distance in length
+    var str = "this is foo bar";
+    str.length - str.replace(/o/g,'').length
+    //>2
diff --git a/gistfile1.js b/gistfile1.js
@@ -25,3 +25,14 @@
        ,str = "this is foo bar";
     for(var i=count=0; i<str.length; count+=+(stringsearch===str[i++]));
      //>count:2
+
+
+#5.
+//element mapping and filtering; not recommended due to its overall resource pre-allocation vs. Pythonian 'generators'
+//provides the position within the string
+    var str = "this is foo bar"
+    str.split('').map( function(e,i){ if(e === 'o') return i;} )
+             .filter(Boolean)
+    //>[9, 10]
+    [9, 10].length
+    //>2
diff --git a/gistfile1.js b/gistfile1.js
@@ -13,12 +13,12 @@
 //You can actually easily observe the EXACT resource usage using **Chrome's profiler** option.
 
 
-//#3.
+#3.
     var stringsearch = "o"
        ,str = "this is foo bar";
     for(var count=-1,index=0; index != -1; count++,index=str.indexOf(stringsearch,index+1) );
      //>count:2
-//#4.
+#4.
 //searching for a single character
 
     var stringsearch = "o"

diff --git a/gistfile1.js b/gistfile1.js
@@ -0,0 +1,27 @@
+//www.lsauer.com 2012
+//Answer to:
+//http://stackoverflow.com/questions/881085/count-the-number-of-occurances-of-a-character-in-a-string-in-javascript/10671743#10671743
+//There are at least four ways. The best option, which should also be the fastest -owing to the native RegEx engine -, is placed at the top. //jsperf.com is currently down, otherwise I would provide you with performance statistics.
+
+#1.
+     ("this is foo bar".match(/o/g)||[]).length
+     //>2
+#2.
+    "this is foo bar".split("o").length-1
+     //>2
+//split is not recommended. Resource hungry. Allocates new instances of 'Array' for each match. Don't try that for a >100MB file via FileReader. 
+//You can actually easily observe the EXACT resource usage using **Chrome's profiler** option.
+
+
+//#3.
+    var stringsearch = "o"
+       ,str = "this is foo bar";
+    for(var count=-1,index=0; index != -1; count++,index=str.indexOf(stringsearch,index+1) );
+     //>count:2
+//#4.
+//searching for a single character
+
+    var stringsearch = "o"
+       ,str = "this is foo bar";
+    for(var i=count=0; i<str.length; count+=+(stringsearch===str[i++]));
+     //>count:2
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