如何在 matplotlib 条形图上注释错误值

Question

我有以下问题：

我想用条形高度（y 值）和误差线高度（误差值）来注释我的条形图 - 具有标准误差线。

我找到了注释条形图的链接Annotate bars with values on Pandas bar plots。建议的策略迭代 Axes Patches 并获取补丁高度以检索 y 值，但我没有找到任何可以提取错误值的东西。

我想得到以下结果：

Answer 1

在下面，考虑到不对称 yerror，我已经修改了 bar_label 以执行与您所要求的类似的操作。

编辑代码末尾的'%d[%d,%d]' % (value,err[0,1],err[1,1])，以您想要的任何格式显示错误。即，使用'%.2f$\pm$%.2f' % (value,err[0,1]) 来显示对称错误。通过调整 err 矩阵索引，也可以轻松考虑 xerrors。

import itertools
def bar_label(container, labels=None, *, fmt="%g", label_type="edge",
              padding=0, **kwargs):

    # want to know whether to put label on positive or negative direction
    # cannot use np.sign here because it will return 0 if x == 0
    def sign(x):
        return 1 if x >= 0 else -1

    bars = container.patches
    errorbar = container.errorbar
    datavalues = container.datavalues
    orientation = container.orientation

    if errorbar:
        # check "ErrorbarContainer" for the definition of these elements
        lines = errorbar.lines  # attribute of "ErrorbarContainer" (tuple)
        barlinecols = lines[2]  # 0: data_line, 1: caplines, 2: barlinecols
        barlinecol = barlinecols[0]  # the "LineCollection" of error bars
        errs = barlinecol.get_segments()
    else:
        errs = []

    if labels is None:
        labels = []

    annotations = []

    for bar, err, dat, lbl in itertools.zip_longest(
        bars, errs, datavalues, labels
    ):
        (x0, y0), (x1, y1) = bar.get_bbox().get_points()
        xc, yc = (x0 + x1) / 2, (y0 + y1) / 2

        if orientation == "vertical":
            extrema = max(y0, y1) if dat >= 0 else min(y0, y1)
            length = abs(y0 - y1)
        elif orientation == "horizontal":
            extrema = max(x0, x1) if dat >= 0 else min(x0, x1)
            length = abs(x0 - x1)

        if err is None:
            endpt = extrema
        elif orientation == "vertical":
            endpt = err[:, 1].max() if dat >= 0 else err[:, 1].min()
        elif orientation == "horizontal":
            endpt = err[:, 0].max() if dat >= 0 else err[:, 0].min()

        if label_type == "center":
            value = sign(dat) * length
        elif label_type == "edge":
            value = extrema

        if label_type == "center":
            xy = xc, yc
        elif label_type == "edge" and orientation == "vertical":
            xy = xc, endpt
        elif label_type == "edge" and orientation == "horizontal":
            xy = endpt, yc

        if orientation == "vertical":
            xytext = 0, sign(dat) * padding
        else:
            xytext = sign(dat) * padding, 0

        if label_type == "center":
            ha, va = "center", "center"
        elif label_type == "edge":
            if orientation == "vertical":
                ha = 'center'
                va = 'top' if dat < 0 else 'bottom'  # also handles NaN
            elif orientation == "horizontal":
                ha = 'right' if dat < 0 else 'left'  # also handles NaN
                va = 'center'

        if np.isnan(dat):
            lbl = ''

        annotation = plt.annotate('%d[%d,%d]' % (value,err[0,1],err[1,1]), #fmt % value if lbl is None else lbl,
                                  xy, xytext, textcoords="offset points",
                                  ha=ha, va=va, **kwargs)
        annotations.append(annotation)

    return annotations