Document D3 number and date format strings

For getredash/redash#6370

src/pages/kb/user-guide/visualizations/formatting-axis.md

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+---
+category: visualizations
+parent_category: user-guide
+title: Formatting Axis in Visualizations
+toc: true
+slug: formatting-axis
+---
+
+Visualizations X and Y axis values are formatted with D3. Below you can find examples for the various format options.
+
+## Numbers
+
+The general form of a number specification is:
+
+```
+[​[fill]align][sign][symbol][0][width][,][.precision][~][type]
+```
+
+_fill_ can be any character. The presence of a fill character is signaled by the _align_ character following it, which must be one of the following:
+
+- `>` - Forces the field to be right-aligned within the available space. (Default behavior).
+- `<` - Forces the field to be left-aligned within the available space.
+- `^` - Forces the field to be centered within the available space.
+- `=` - like `>`, but with any sign and symbol to the left of any padding.
+
+_sign_ can be:
+
+- `-` - nothing for zero or positive and a minus sign for negative. (Default behavior.)
+- `+` - a plus sign for zero or positive and a minus sign for negative.
+- `(` - nothing for zero or positive and parentheses for negative.
+- ` ` (space) - a space for zero or positive and a minus sign for negative.
+
+_symbol_ can be:
+
+- `$` - apply currency symbols per the locale definition.
+- `#` - for binary, octal, or hexadecimal notation, prefix by `0b`, `0o`, or `0x`, respectively.
+
+The _zero_ (`0`) option enables zero-padding; this implicitly sets _fill_ to `0` and _align_ to `=`. The _width_ defines the minimum field width; if not specified, then the width will be determined by the content. The _comma_ (`,`) option enables the use of a group separator, such as a comma for thousands.
+
+Depending on the _type_, the _precision_ either indicates the number of digits that follow the decimal point (types `f` and `%`), or the number of significant digits (types `​`, `e`, `g`, `r`, `s` and `p`). If the precision is not specified, it defaults to 6 for all types except `​` (none), which defaults to 12. Precision is ignored for integer formats (types `b`, `o`, `d`, `x`, and `X`) and character data (type `c`).
+
+The `~` option trims insignificant trailing zeros across all format types. This is most commonly used in conjunction with types `r`, `e`, `s` and `%`.
+
+The available _type_ values are:
+
+- `e` - exponent notation.
+- `f` - fixed point notation.
+- `g` - either decimal or exponent notation, rounded to significant digits.
+- `r` - decimal notation, rounded to significant digits.
+- `s` - decimal notation with an "SI prefix" (`k`, `M`, `G`, ...), rounded to significant digits.
+- `%` - multiply by 100, and then decimal notation with a percent sign.
+- `p` - multiply by 100, round to significant digits, and then decimal notation with a percent sign.
+- `b` - binary notation, rounded to integer.
+- `o` - octal notation, rounded to integer.
+- `d` - decimal notation, rounded to integer.
+- `x` - hexadecimal notation, using lower-case letters, rounded to integer.
+- `X` - hexadecimal notation, using upper-case letters, rounded to integer.
+- `c` - character data, for a string of text.
+
+The type `​` (none) is also supported as shorthand for `~g` (with a default precision of 12 instead of 6), and the type `n` is shorthand for `,g`. For the `g`, `n` and `​` (none) types, decimal notation is used if the resulting string would have _precision_ or fewer digits; otherwise, exponent notation is used. For example:
+
+## Time
+
+The time format string may contain the following directives:
+
+- `%a` - abbreviated weekday name.\*
+- `%A` - full weekday name.\*
+- `%b` - abbreviated month name.\*
+- `%B` - full month name.\*
+- `%c` - the locale’s date and time, such as `%x, %X`.\*
+- `%d` - zero-padded day of the month as a decimal number [01,31].
+- `%e` - space-padded day of the month as a decimal number [ 1,31]; equivalent to `%_d`.
+- `%f` - microseconds as a decimal number [000000, 999999].
+- `%g` - ISO 8601 week-based year without century as a decimal number [00,99].
+- `%G` - ISO 8601 week-based year with century as a decimal number.
+- `%H` - hour (24-hour clock) as a decimal number [00,23].
+- `%I` - hour (12-hour clock) as a decimal number [01,12].
+- `%j` - day of the year as a decimal number [001,366].
+- `%m` - month as a decimal number [01,12].
+- `%M` - minute as a decimal number [00,59].
+- `%L` - milliseconds as a decimal number [000, 999].
+- `%p` - either AM or PM.\*
+- `%q` - quarter of the year as a decimal number [1,4].
+- `%Q` - milliseconds since UNIX epoch.
+- `%s` - seconds since UNIX epoch.
+- `%S` - second as a decimal number [00,61].
+- `%u` - Monday-based (ISO 8601) weekday as a decimal number [1,7].
+- `%U` - Sunday-based week of the year as a decimal number [00,53].
+- `%V` - ISO 8601 week of the year as a decimal number [01, 53].
+- `%w` - Sunday-based weekday as a decimal number [0,6].
+- `%W` - Monday-based week of the year as a decimal number [00,53].
+- `%x` - the locale’s date, such as `%-m/%-d/%Y`.\*
+- `%X` - the locale’s time, such as `%-I:%M:%S %p`.\*
+- `%y` - year without century as a decimal number [00,99].
+- `%Y` - year with century as a decimal number, such as `1999`.
+- `%Z` - time zone offset, such as `-0700`, `-07:00`, `-07`, or `Z`.
+- `%%` - a literal percent sign (`%`).
+
+Directives marked with an asterisk (\*) may be affected by the locale definition.
+
+The `%` sign indicating a directive may be immediately followed by a padding modifier:
+
+- `0` - zero-padding
+- `_` - space-padding
+- `-` - disable padding
+
+If no padding modifier is specified, the default is `0` for all directives except `%e`, which defaults to `_`.