在matplotlib条形图上添加值标签

Question

我被困在感觉上应该相对容易的东西上。我在下面提供的代码是基于我正在从事的一个较大项目的示例。我认为没有理由发布所有详细信息，因此请原样接受我带来的数据结构。

[基本上，我正在创建一个条形图，我可以弄清楚如何在条形图上（在条形图的中心或上方）添加值标签。一直在网上查看示例，但是在我自己的代码上实现没有成功。我相信解决方案是使用“文本”或“注释”，但是我：a）不知道使用哪个（通常来说，还没有弄清楚何时使用哪个）。b）看不到要显示值标签。感谢您的帮助，下面是我的代码。预先感谢！

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
pd.set_option('display.mpl_style', 'default') 
%matplotlib inline

# Bring some raw data.
frequencies = [6, 16, 75, 160, 244, 260, 145, 73, 16, 4, 1]

# In my original code I create a series and run on that, 
# so for consistency I create a series from the list.
freq_series = pd.Series.from_array(frequencies)

x_labels = [108300.0, 110540.0, 112780.0, 115020.0, 117260.0, 119500.0, 
            121740.0, 123980.0, 126220.0, 128460.0, 130700.0]

# Plot the figure.
plt.figure(figsize=(12, 8))
fig = freq_series.plot(kind='bar')
fig.set_title('Amount Frequency')
fig.set_xlabel('Amount ($)')
fig.set_ylabel('Frequency')
fig.set_xticklabels(x_labels)

Answer 1

首先freq_series.plot返回一个轴not一个数字，以便使我的回答更加清楚，我已更改了给定的代码，将其称为ax而不是fig，以便与其他代码示例。

您可以从ax.patches成员那里获得图中绘制的柱线的列表。然后，您可以使用this matplotlib gallery example中演示的技术通过matplotlib方法添加标签。

ax.text

这将产生一个标记的图，看起来像：

<< img src =“ https://image.soinside.com/eyJ1cmwiOiAiaHR0cHM6Ly9pLnN0YWNrLmltZ3VyLmNvbS8wUk1hei5wbmcifQ==” alt =“在此处输入图像描述”>

Answer 2

基于ax.text中提到的功能，我发现了一种非常普遍适用的将标签放置在条形图上的解决方案。

不幸的是，其他解决方案在许多情况下不起作用，因为标签和条形之间的间距是

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt

# Bring some raw data.
frequencies = [6, 16, 75, 160, 244, 260, 145, 73, 16, 4, 1]
# In my original code I create a series and run on that, 
# so for consistency I create a series from the list.
freq_series = pd.Series.from_array(frequencies)

x_labels = [108300.0, 110540.0, 112780.0, 115020.0, 117260.0, 119500.0,
            121740.0, 123980.0, 126220.0, 128460.0, 130700.0]

# Plot the figure.
plt.figure(figsize=(12, 8))
ax = freq_series.plot(kind='bar')
ax.set_title('Amount Frequency')
ax.set_xlabel('Amount ($)')
ax.set_ylabel('Frequency')
ax.set_xticklabels(x_labels)

rects = ax.patches

# Make some labels.
labels = ["label%d" % i for i in xrange(len(rects))]

for rect, label in zip(rects, labels):
    height = rect.get_height()
    ax.text(rect.get_x() + rect.get_width() / 2, height + 5, label,
            ha='center', va='bottom')

或this answer to another question。前者仅适用于狭窄范围的值，而后者在一个绘图中给出的间距不一致。对数轴都不能很好地工作。

我提出的解决方案与比例无关（即，无论大小），甚至正确地为负值和对数比例放置标签，因为它使用可视单位given in absolute units of the bars进行偏移。

我添加了一个负数以展示这种情况下标签的正确放置。

每个条形的高度值用作其标签。其他标签可以通过scaled by the height of the bar轻松使用。

points

编辑：我已经提取了一个功能中的相关功能，如Simon's for rect, label in zip(rects, labels) snippet所建议。

这将产生以下输出：

for rect, label in zip(rects, labels)

并且使用对数标度（以及对输入数据的一些调整以显示对数标度），这是结果：

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt

# Bring some raw data.
frequencies = [6, -16, 75, 160, 244, 260, 145, 73, 16, 4, 1]

# In my original code I create a series and run on that,
# so for consistency I create a series from the list.
freq_series = pd.Series.from_array(frequencies)

x_labels = [108300.0, 110540.0, 112780.0, 115020.0, 117260.0, 119500.0,
            121740.0, 123980.0, 126220.0, 128460.0, 130700.0]

# Plot the figure.
plt.figure(figsize=(12, 8))
ax = freq_series.plot(kind='bar')
ax.set_title('Amount Frequency')
ax.set_xlabel('Amount ($)')
ax.set_ylabel('Frequency')
ax.set_xticklabels(x_labels)


def add_value_labels(ax, spacing=5):
    """Add labels to the end of each bar in a bar chart.

    Arguments:
        ax (matplotlib.axes.Axes): The matplotlib object containing the axes
            of the plot to annotate.
        spacing (int): The distance between the labels and the bars.
    """

    # For each bar: Place a label
    for rect in ax.patches:
        # Get X and Y placement of label from rect.
        y_value = rect.get_height()
        x_value = rect.get_x() + rect.get_width() / 2

        # Number of points between bar and label. Change to your liking.
        space = spacing
        # Vertical alignment for positive values
        va = 'bottom'

        # If value of bar is negative: Place label below bar
        if y_value < 0:
            # Invert space to place label below
            space *= -1
            # Vertically align label at top
            va = 'top'

        # Use Y value as label and format number with one decimal place
        label = "{:.1f}".format(y_value)

        # Create annotation
        ax.annotate(
            label,                      # Use `label` as label
            (x_value, y_value),         # Place label at end of the bar
            xytext=(0, space),          # Vertically shift label by `space`
            textcoords="offset points", # Interpret `xytext` as offset in points
            ha='center',                # Horizontally center label
            va=va)                      # Vertically align label differently for
                                        # positive and negative values.


# Call the function above. All the magic happens there.
add_value_labels(ax)

plt.savefig("image.png")

Answer 3

基于以上（很好！）的答案，我们还可以通过一些调整就可以制作出水平条形图：

barnhillec

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Answer 4

如果只想在条形上方添加数据点，则可以轻松地通过以下方式进行：