Add support for F, r and p format types.

`F` is an alias for `f`. `r` is a new format type that rounds the input number,
treating the precision field as the desired number of significant digits. This
is similar to `g`, except it never uses exponent notation. `p` is equivalent to
`r`, except it outputs a percentage, as with `%`.

d3.js

@@ -350,7 +350,7 @@ function d3_dispatch(type) {
 
   return dispatch;
 };
-// TODO align, type
+// TODO align
 d3.format = function(specifier) {
   var match = d3_format_re.exec(specifier),
       fill = match[1] || " ",
@@ -360,36 +360,35 @@ d3.format = function(specifier) {
       comma = match[7],
       precision = match[8],
       type = match[9],
-      percentage = false;
+      percentage = false,
+      integer = false;
 
-  if (type === "n") {
-    comma = true;
-    type = "g";
-  } else if (type === "%") {
-    percentage = true;
-    type = "f";
-  }
   if (precision) precision = precision.substring(1);
+
   if (zfill) {
     fill = "0"; // TODO align = "=";
     if (comma) width -= Math.floor((width - 1) / 4);
   }
-  if (type === "d") precision = "0";
+
+  switch (type) {
+    case "F": type = "f"; break;
+    case "n": comma = true; type = "g"; break;
+    case "%": percentage = true; type = "f"; break;
+    case "p": percentage = true; type = "r"; break;
+    case "d": integer = true; precision = "0"; break;
+  }
+
+  type = d3_format_types[type] || d3_format_typeDefault;
 
   return function(value) {
     var number = percentage ? value * 100 : +value,
         negative = (number < 0) && (number = -number) ? "\u2212" : sign;
 
     // Return the empty string for floats formatted as ints.
-    if ((type === "d") && (number % 1)) return "";
+    if (integer && (number % 1)) return "";
 
     // Convert the input value to the desired precision.
-    value = type === "g" ? number.toPrecision(precision).replace(/\.0+$/, "")
-      : type === "G" ? number.toPrecision(precision).replace(/\.0+$/, "").replace("e", "E")
-      : type === "e" ? number.toExponential(precision)
-      : type === "E" ? number.toExponential(precision).replace("e", "E")
-      : type === "f" ? number.toFixed(precision)
-      : "" + number;
+    value = type(number, precision);
 
     // If the fill character is 0, the sign and group is applied after the fill.
     if (zfill) {
@@ -415,6 +414,22 @@ d3.format = function(specifier) {
 // [[fill]align][sign][#][0][width][,][.precision][type]
 var d3_format_re = /(?:([^{])?([<>=^]))?([+\- ])?(#)?(0)?([0-9]+)?(,)?(\.[0-9]+)?([a-zA-Z%])?/;
 
+var d3_format_types = {
+  g: function(x, p) { return x.toPrecision(p).replace(/\.0+$/, ""); },
+  G: function(x, p) { return d3_format_types.g(x, p).replace("e", "E"); },
+  e: function(x, p) { return x.toExponential(p); },
+  E: function(x, p) { return d3_format_types.e(x, p).replace("e", "E"); },
+  f: function(x, p) { return x.toFixed(p); },
+  r: function(x, p) {
+    var n = 1 + Math.floor(1e-15 + Math.log(x) / Math.LN10);
+    return d3.round(x, p - n).toFixed(Math.max(0, p - n));
+  }
+};
+
+function d3_format_typeDefault(x) {
+  return x + "";
+}
+
 // Apply comma grouping for thousands.
 function d3_format_group(value) {
   var i = value.lastIndexOf("."),

src/core/format.js

@@ -1,4 +1,4 @@
-// TODO align, type
+// TODO align
 d3.format = function(specifier) {
   var match = d3_format_re.exec(specifier),
       fill = match[1] || " ",
@@ -8,36 +8,35 @@ d3.format = function(specifier) {
       comma = match[7],
       precision = match[8],
       type = match[9],
-      percentage = false;
+      percentage = false,
+      integer = false;
 
-  if (type === "n") {
-    comma = true;
-    type = "g";
-  } else if (type === "%") {
-    percentage = true;
-    type = "f";
-  }
   if (precision) precision = precision.substring(1);
+
   if (zfill) {
     fill = "0"; // TODO align = "=";
     if (comma) width -= Math.floor((width - 1) / 4);
   }
-  if (type === "d") precision = "0";
+
+  switch (type) {
+    case "F": type = "f"; break;
+    case "n": comma = true; type = "g"; break;
+    case "%": percentage = true; type = "f"; break;
+    case "p": percentage = true; type = "r"; break;
+    case "d": integer = true; precision = "0"; break;
+  }
+
+  type = d3_format_types[type] || d3_format_typeDefault;
 
   return function(value) {
     var number = percentage ? value * 100 : +value,
         negative = (number < 0) && (number = -number) ? "\u2212" : sign;
 
     // Return the empty string for floats formatted as ints.
-    if ((type === "d") && (number % 1)) return "";
+    if (integer && (number % 1)) return "";
 
     // Convert the input value to the desired precision.
-    value = type === "g" ? number.toPrecision(precision).replace(/\.0+$/, "")
-      : type === "G" ? number.toPrecision(precision).replace(/\.0+$/, "").replace("e", "E")
-      : type === "e" ? number.toExponential(precision)
-      : type === "E" ? number.toExponential(precision).replace("e", "E")
-      : type === "f" ? number.toFixed(precision)
-      : "" + number;
+    value = type(number, precision);
 
     // If the fill character is 0, the sign and group is applied after the fill.
     if (zfill) {
@@ -63,6 +62,22 @@ d3.format = function(specifier) {
 // [[fill]align][sign][#][0][width][,][.precision][type]
 var d3_format_re = /(?:([^{])?([<>=^]))?([+\- ])?(#)?(0)?([0-9]+)?(,)?(\.[0-9]+)?([a-zA-Z%])?/;
 
+var d3_format_types = {
+  g: function(x, p) { return x.toPrecision(p).replace(/\.0+$/, ""); },
+  G: function(x, p) { return d3_format_types.g(x, p).replace("e", "E"); },
+  e: function(x, p) { return x.toExponential(p); },
+  E: function(x, p) { return d3_format_types.e(x, p).replace("e", "E"); },
+  f: function(x, p) { return x.toFixed(p); },
+  r: function(x, p) {
+    var n = 1 + Math.floor(1e-15 + Math.log(x) / Math.LN10);
+    return d3.round(x, p - n).toFixed(Math.max(0, p - n));
+  }
+};
+
+function d3_format_typeDefault(x) {
+  return x + "";
+}
+
 // Apply comma grouping for thousands.
 function d3_format_group(value) {
   var i = value.lastIndexOf("."),

tests/test-format.js

@@ -94,10 +94,10 @@ console.log("  ", d3.format(".1f")(0.49));
 console.log("  ", d3.format(".2f")(0.449));
 console.log("  ", d3.format(".3f")(0.4449));
 console.log("  ", d3.format(".5f")(0.444449));
-console.log("  ", d3.format(".1f")(100));
-console.log("  ", d3.format(".2f")(100));
-console.log("  ", d3.format(".3f")(100));
-console.log("  ", d3.format(".5f")(100));
+console.log("  ", d3.format(".1F")(100));
+console.log("  ", d3.format(".2F")(100));
+console.log("  ", d3.format(".3F")(100));
+console.log("  ", d3.format(".5F")(100));
 console.log("");
 
 console.log("precision (significant digits):");
@@ -112,6 +112,21 @@ console.log("  ", d3.format(".3g")(100));
 console.log("  ", d3.format(".5g")(100));
 console.log("");
 
+console.log("precision and rounding (significant digits):");
+console.log("  ", d3.format(".1r")(0.049));
+console.log("  ", d3.format(".1r")(0.49));
+console.log("  ", d3.format(".2r")(0.449));
+console.log("  ", d3.format(".3r")(0.4449));
+console.log("  ", d3.format(".5r")(0.444449));
+console.log("  ", d3.format("r")(123.45));
+console.log("  ", d3.format(".1r")(123.45));
+console.log("  ", d3.format(".2r")(123.45));
+console.log("  ", d3.format(".3r")(123.45));
+console.log("  ", d3.format(".4r")(123.45));
+console.log("  ", d3.format(".5r")(123.45));
+console.log("  ", d3.format(".6r")(123.45));
+console.log("");
+
 console.log("precision and grouping with space fill:");
 console.log("  ", d3.format("10,.1f")(123456.49));
 console.log("  ", d3.format("10,.2f")(1234567.449));
@@ -128,7 +143,7 @@ console.log("  ", d3.format("f")(42));
 console.log("");
 
 console.log("int type passed float:");
-console.log("  ", d3.format("d")(4.2));
+console.log(d3.format("d")(4.2));
 console.log("");
 
 console.log("number:");
@@ -146,13 +161,23 @@ console.log("");
 
 console.log("percentage:");
 console.log("  ", d3.format("%")(0));
-console.log("  ", d3.format("%")(42));
-console.log("  ", d3.format("%")(42000000));
-console.log("  ", d3.format("%")(420000000));
-console.log("  ", d3.format("%")(-4));
-console.log("  ", d3.format("%")(-42));
-console.log("  ", d3.format("%")(-4200000));
-console.log("  ", d3.format("%")(-42000000));
+console.log("  ", d3.format("%")(.042));
+console.log("  ", d3.format("%")(.42));
+console.log("  ", d3.format("%")(4.2));
+console.log("  ", d3.format("%")(-.042));
+console.log("  ", d3.format("%")(-.42));
+console.log("  ", d3.format("%")(-4.2));
+console.log("");
+
+console.log("percentage with rounding and sign:");
+console.log("  ", d3.format("+.2p")(.00123));
+console.log("  ", d3.format("+.2p")(.0123));
+console.log("  ", d3.format("+.2p")(.123));
+console.log("  ", d3.format("+.2p")(1.23));
+console.log("  ", d3.format("+.2p")(-.00123));
+console.log("  ", d3.format("+.2p")(-.0123));
+console.log("  ", d3.format("+.2p")(-.123));
+console.log("  ", d3.format("+.2p")(-1.23));
 console.log("");
 
 console.log("exponent:");

tests/test-format.out

@@ -97,6 +97,20 @@ precision (significant digits):
    100
    100
 
+precision and rounding (significant digits):
+   0.05
+   0.5
+   0.45
+   0.445
+   0.44445
+   123
+   100
+   120
+   123
+   123.5
+   123.45
+   123.450
+
 precision and grouping with space fill:
     123,456.5
    1,234,567.45
@@ -111,7 +125,7 @@ float type passed int:
    42
 
 int type passed float:
-   
+
 
 number:
    0.0042
@@ -127,13 +141,22 @@ number:
 
 percentage:
    0%
-   4200%
-   4200000000%
-   42000000000%
-   −400%
-   −4200%
-   −420000000%
-   −4200000000%
+   4%
+   42%
+   420%
+   −4%
+   −42%
+   −420%
+
+percentage with rounding and sign:
+   +0.12%
+   +1.2%
+   +12%
+   +120%
+   −0.12%
+   −1.2%
+   −12%
+   −120%
 
 exponent:
    0e+0