1 语法

bar(*args, **kwargs)

Call signatures::

bar(x, height, *, align='center', **kwargs)

bar(x, height, width, *, align='center', **kwargs)

bar(x, height, width, bottom, *, align='center', **kwargs)

参数

x : sequence of scalars；bar的条形坐标

height : scalar or sequence of scalars；bar的高度

width : scalar or array-like, optional；bar的宽度，默认值0.8

bottom : scalar or array-like, optional；bar的 y 轴方向的基坐标

align : {'center', 'edge'}, optional, default: 'center'，``align='edge'``.；与x坐标对其方式

center - bar的每条形图中心位于X值位置

edge - bar的每条形图的左边与X值对齐

如果想实现右边界对齐，可以align = ‘edge’，同时将宽度设置为负数即可

color : scalar or array-like, optional；bar faces颜色

edgecolor : scalar or array-like, optional；bar edges颜色

linewidth : scalar or array-like, optional；bar边缘线宽，若为0，则不绘制边

tick_label : string or array-like, optional；bar的刻度标签，Default: None (Use default numeric labels.)

xerr, yerr : scalar or array-like of shape(N,) or shape(2,N), optional；若非None，则在bar端面处添加水平或垂直误差条，其值为+/- sizes的相对误差，如下图所示

当然也可以通过参数进行控制正负误差，

scalar - 所有bar具有 +/- values

shape(N,) - 每一个bar +/- values

shape(2,N) - 每一个bar 都具有单独的 - and + values，lower errors 包含在 First row，upper errors 位于 second row

None - 没有误差项（默认）

ecolor : scalar or array-like, optional, default: 'black'；误差线条的颜色

capsize : scalar, optional；误差条的长度，

log : bool, optional, default: False，若True，设置 y 轴为 log 刻度

orientation : {'vertical', 'horizontal'}, optional；Default: 'vertical'，*This is for internal use only.* Please use `barh` for horizontal bar plots.

2 示例

import numpy as npimport matplotlib.pyplot as pltn = 12x = np.arange(n)y1 = (1 - x / n) * np.random.uniform(0.5, 1.0, n)y2 = (1 - x / n) * np.random.uniform(0.5, 1.0, n)plt.figure('Bar', facecolor='lightgray')plt.title('Bar', fontsize=20)plt.xlabel('x', fontsize=14)plt.ylabel('y', fontsize=14)plt.xticks(x, x + 1)plt.tick_params(labelsize=10)plt.grid(axis='y', linestyle=':')# 绘制barplt.bar(x, y1, 0.9,        ec='white', fc='dodgerblue',        label='Sapltle 1'        )# ec edgecolor; fc facecolor# 绘制bar值for _x, _y in zip(x, y1):    plt.text(_x, _y, '%.2f' % _y,             ha='center', va='bottom', size=8             )plt.bar(x, -y2, 0.9,        ec='white', fc='dodgerblue', alpha=0.5,       label='Sample 2',yerr = x*0.01)for _x, _y in zip(x, y2):    plt.text(_x, -_y, '%.2f' % _y,             ha='center', va='top', size=8)plt.legend()plt.show()

3 help(plt.bar)

Help on function bar in module matplotlib.pyplot:bar(*args, **kwargs)    Make a bar plot.        Call signatures::           bar(x, height, *, align='center', **kwargs)       bar(x, height, width, *, align='center', **kwargs)       bar(x, height, width, bottom, *, align='center', **kwargs)        The bars are positioned at *x* with the given *align* ment. Their    dimensions are given by *width* and *height*. The vertical baseline    is *bottom* (default 0).        Each of *x*, *height*, *width*, and *bottom* may either be a scalar    applying to all bars, or it may be a sequence of length N providing a    separate value for each bar.            Parameters    ----------    x : sequence of scalars        The x coordinates of the bars. See also *align* for the        alignment of the bars to the coordinates.        height : scalar or sequence of scalars        The height(s) of the bars.        width : scalar or array-like, optional        The width(s) of the bars (default: 0.8).        bottom : scalar or array-like, optional        The y coordinate(s) of the bars bases (default: 0).        align : {
    'center', 'edge'}, optional, default: 'center'        Alignment of the bars to the *x* coordinates:            - 'center': Center the base on the *x* positions.        - 'edge': Align the left edges of the bars with the *x* positions.            To align the bars on the right edge pass a negative *width* and        ``align='edge'``.        Returns    -------    container : `.BarContainer`        Container with all the bars and optionally errorbars.        Other Parameters    ----------------    color : scalar or array-like, optional        The colors of the bar faces.        edgecolor : scalar or array-like, optional        The colors of the bar edges.        linewidth : scalar or array-like, optional        Width of the bar edge(s). If 0, don't draw edges.        tick_label : string or array-like, optional        The tick labels of the bars.        Default: None (Use default numeric labels.)        xerr, yerr : scalar or array-like of shape(N,) or shape(2,N), optional        If not *None*, add horizontal / vertical errorbars to the bar tips.        The values are +/- sizes relative to the data:            - scalar: symmetric +/- values for all bars        - shape(N,): symmetric +/- values for each bar        - shape(2,N): Separate - and + values for each bar. First row            contains the lower errors, the second row contains the            upper errors.        - *None*: No errorbar. (Default)            See :ref:`sphx_glr_gallery_statistics_errorbar_features.py`        for an example on the usage of ``xerr`` and ``yerr``.        ecolor : scalar or array-like, optional, default: 'black'        The line color of the errorbars.        capsize : scalar, optional       The length of the error bar caps in points.       Default: None, which will take the value from       :rc:`errorbar.capsize`.        error_kw : dict, optional        Dictionary of kwargs to be passed to the `~.Axes.errorbar`        method. Values of *ecolor* or *capsize* defined here take        precedence over the independent kwargs.        log : bool, optional, default: False        If *True*, set the y-axis to be log scale.        orientation : {
    'vertical',  'horizontal'}, optional        *This is for internal use only.* Please use `barh` for        horizontal bar plots. Default: 'vertical'.        See also    --------    barh: Plot a horizontal bar plot.        Notes    -----    The optional arguments *color*, *edgecolor*, *linewidth*,    *xerr*, and *yerr* can be either scalars or sequences of    length equal to the number of bars.  This enables you to use    bar as the basis for stacked bar charts, or candlestick plots.    Detail: *xerr* and *yerr* are passed directly to    :meth:`errorbar`, so they can also have shape 2xN for    independent specification of lower and upper errors.        Other optional kwargs:          agg_filter: a filter function, which takes a (m, n, 3) float array and a dpi value, and returns a (m, n, 3) array       alpha: float or None       animated: bool       antialiased or aa: bool or None       capstyle: ['butt' | 'round' | 'projecting']       clip_box: a `.Bbox` instance       clip_on: bool       clip_path: [(`~matplotlib.path.Path`, `.Transform`) | `.Patch` | None]       color: matplotlib color spec      contains: a callable function       edgecolor or ec: mpl color spec, None, 'none', or 'auto'       facecolor or fc: mpl color spec, or None for default, or 'none' for no color       figure: a `.Figure` instance       fill: bool       gid: an id string       hatch: ['/' | '\\' | '|' | '-' | '+' | 'x' | 'o' | 'O' | '.' | '*']       joinstyle: ['miter' | 'round' | 'bevel']       label: object       linestyle or ls: ['solid' | 'dashed', 'dashdot', 'dotted' | (offset, on-off-dash-seq) | ``'-'`` | ``'--'`` | ``'-.'`` | ``':'`` | ``'None'`` | ``' '`` | ``''``]      linewidth or lw: float or None for default       path_effects: `.AbstractPathEffect`       picker: [None | bool | float | callable]       rasterized: bool or None       sketch_params: (scale: float, length: float, randomness: float)       snap: bool or None       transform: `.Transform`       url: a url string       visible: bool       zorder: float         .. note::        In addition to the above described arguments, this function can take a        **data** keyword argument. If such a **data** argument is given, the        following arguments are replaced by **data[
     
      ]**:            * All arguments with the following names: 'bottom', 'color', 'ecolor', 'edgecolor', 'height', 'left', 'linewidth', 'tick_label', 'width', 'x', 'xerr', 'y', 'yerr'.        * All positional arguments.

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