基于matplotlib的数据可视化 - 柱状图bar

柱状图bar

柱状图常用表现形式为：

plt.bar(水平坐标数组，高度数组，宽度比例，ec=勾边色，c=填充色，label=图例标签)

注：当高度值为负数时，柱形向下

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 np
import matplotlib.pyplot as plt

n = 12
x = 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bar
plt.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[<arg>]**:

        * All arguments with the following names: 'bottom', 'color', 'ecolor', 'edgecolor', 'height', 'left', 'linewidth', 'tick_label', 'width', 'x', 'xerr', 'y', 'yerr'.
        * All positional arguments.