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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[ENH?] EngFormatter: add the possibility to remove the space before the SI prefix ","articleBody":"Discussing with some of my colleagues who are using other plotting softwares than Matplotlib, I noticed that their formatting of the engineering notation is a bit different from the one implemented in `ticker.EngFormatter`. Some softwares append directly the prefix/unit to the tick value (e.g. \"1.23µs\", vs \"1.23 µs\" with Matplotlib). I am not sure it is really OK from the (English) typography point of view but I guess they are doing this due to the rather limited ticklablel space. \n\nI wonder how interesting it may be to add such a possibility to the `EngFormatter` in Matplotlib. As some users may prefer \"1.23µs\" over \"1.23 µs\", I would say it's worth adding it to `EngFormatter`. \n\nIf it is added to `EngFormatter`, I guess the major pitfall would be the default values… IMO, the current behavior of Matplotlib is the best one when `EngFormatter` is instantiated with a unit. However, when it is instantatied without unit (`unit=\"\"`), I wouldn't be categorical about the fact that \"1.23 µ\" is better than \"1.23µ\". So I don't really know if one should use by default a space separator between the value and the prefix/unit, or not…\n\nI wrote a small demonstration of what could be easily done with the `EngFormatter`class (keeping the current Matplotlib behavior as the default one). It is \u003e 100 lines because I directly copy-pasted the source code of `ticker.EngFormatter`. I've put the changes between `\u003cENH\u003e` and `\u003c\\ENH\u003e` tags. NB: the code includes a bug fix similar to PR #6014 . \n\n``` python\nfrom __future__ import division, print_function, unicode_literals\nimport decimal\nimport math\nimport numpy as np\nfrom matplotlib.ticker import Formatter\n\n\n# Proposed \"enhancement\" of the EngFormatter\nclass EnhancedEngFormatter(Formatter):\n    \"\"\"\n    Formats axis values using engineering prefixes to represent powers of 1000,\n    plus a specified unit, e.g., 10 MHz instead of 1e7.\n    \"\"\"\n\n    # the unicode for -6 is the greek letter mu\n    # commeted here due to bug in pep8\n    # (https://github.com/jcrocholl/pep8/issues/271)\n\n    # The SI engineering prefixes\n    ENG_PREFIXES = {\n        -24: \"y\",\n        -21: \"z\",\n        -18: \"a\",\n        -15: \"f\",\n        -12: \"p\",\n         -9: \"n\",\n         -6: \"\\u03bc\",\n         -3: \"m\",\n          0: \"\",\n          3: \"k\",\n          6: \"M\",\n          9: \"G\",\n         12: \"T\",\n         15: \"P\",\n         18: \"E\",\n         21: \"Z\",\n         24: \"Y\"\n    }\n\n    def __init__(self, unit=\"\", places=None, space_sep=True):\n        \"\"\" Parameters\n            ----------\n            unit: str (default: \"\")\n                Unit symbol to use.\n\n            places: int (default: None)\n                Number of digits after the decimal point.\n                If it is None, falls back to the floating point format '%g'.\n\n            space_sep: boolean (default: True)\n                If True, a (single) space is used between the value and the\n                prefix/unit, else the prefix/unit is directly appended to the\n                value.\n        \"\"\"\n        self.unit = unit\n        self.places = places\n        # \u003cENH\u003e\n        if space_sep is True:\n            self.sep = \" \"  # 1 space\n        else:\n            self.sep = \"\"  # no space\n        # \u003c\\ENH\u003e\n\n    def __call__(self, x, pos=None):\n        s = \"%s%s\" % (self.format_eng(x), self.unit)\n        return self.fix_minus(s)\n\n    def format_eng(self, num):\n        \"\"\" Formats a number in engineering notation, appending a letter\n        representing the power of 1000 of the original number. Some examples:\n\n        \u003e\u003e\u003e format_eng(0)       # for self.places = 0\n        '0'\n\n        \u003e\u003e\u003e format_eng(1000000) # for self.places = 1\n        '1.0 M'\n\n        \u003e\u003e\u003e format_eng(\"-1e-6\") # for self.places = 2\n        u'-1.00 \\u03bc'\n\n        @param num: the value to represent\n        @type num: either a numeric value or a string that can be converted to\n                   a numeric value (as per decimal.Decimal constructor)\n\n        @return: engineering formatted string\n        \"\"\"\n\n        dnum = decimal.Decimal(str(num))\n\n        sign = 1\n\n        if dnum \u003c 0:\n            sign = -1\n            dnum = -dnum\n\n        if dnum != 0:\n            pow10 = decimal.Decimal(int(math.floor(dnum.log10() / 3) * 3))\n        else:\n            pow10 = decimal.Decimal(0)\n\n        pow10 = pow10.min(max(self.ENG_PREFIXES.keys()))\n        pow10 = pow10.max(min(self.ENG_PREFIXES.keys()))\n\n        prefix = self.ENG_PREFIXES[int(pow10)]\n\n        mant = sign * dnum / (10 ** pow10)\n\n        # \u003cENH\u003e\n        if self.places is None:\n            format_str = \"%g{sep:s}%s\".format(sep=self.sep)\n        elif self.places == 0:\n            format_str = \"%i{sep:s}%s\".format(sep=self.sep)\n        elif self.places \u003e 0:\n            format_str = \"%.{p:i}f{sep:s}%s\".format(p=self.places,\n                                                    sep=self.sep)\n        # \u003c\\ENH\u003e\n\n        formatted = format_str % (mant, prefix)\n\n        formatted = formatted.strip()\n        if (self.unit != \"\") and (prefix == self.ENG_PREFIXES[0]):\n            # \u003cENH\u003e\n            formatted = formatted + self.sep\n            # \u003c\\ENH\u003e\n\n        return formatted\n\n\n# DEMO\ndef demo_formatter(**kwargs):\n    \"\"\" Print the strings produced by the EnhancedEngFormatter for a list of\n        arbitrary test values.\n    \"\"\"\n    TEST_VALUES = [1.23456789e-6, 0.1, 1, 999.9, 1001]\n    unit = kwargs.get('unit', \"\")\n    space_sep = kwargs.get('space_sep', True)\n    formatter = EnhancedEngFormatter(**kwargs)\n\n    print(\"\\n[Case: unit='{u:s}' \u0026 space_sep={s}]\".format(u=unit, s=space_sep))\n    print(*[\"{tst};\".format(tst=formatter(value)) for value in TEST_VALUES])\n\nif __name__ == '__main__':\n    \"\"\" Matplotlib current behavior (w/ space separator) \"\"\"\n    demo_formatter(unit=\"s\", space_sep=True)\n    # \u003e\u003e 1.23457 μs; 100 ms; 1 s; 999.9 s; 1.001 ks;\n    demo_formatter(unit=\"\", space_sep=True)\n    # \u003e\u003e 1.23457 μ; 100 m; 1; 999.9; 1.001 k;\n\n    \"\"\" New possibility (w/o space separator) \"\"\"\n    demo_formatter(unit=\"s\", space_sep=False)\n    # \u003e\u003e 1.23457μs; 100ms; 1s; 999.9s; 1.001ks;\n    demo_formatter(unit=\"\", space_sep=False)\n    # \u003e\u003e 1.23457μ; 100m; 1; 999.9; 1.001k;\n```\n","author":{"url":"https://github.com/afvincent","@type":"Person","name":"afvincent"},"datePublished":"2016-06-04T22:27:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":10},"url":"https://github.com/6533/matplotlib/issues/6533"}