Question

问题

下面的代码是散景文档中的vbar chart示例。在这个例子中我无法理解。

其中'cyl_mfr'来自factor_cmap（）和vbar（）？



'mpg_mean'，是否计算'mpg'列的平均值？如果那样的话   为什么'mpg_sum'不起作用？

我想像这个例子一样创建自己的vbar图表。

代码

from bokeh.io import show, output_file
from bokeh.models import ColumnDataSource, HoverTool
from bokeh.plotting import figure
from bokeh.palettes import Spectral5
from bokeh.sampledata.autompg import autompg_clean as df
from bokeh.transform import factor_cmap

output_file("bars.html")

df.cyl = df.cyl.astype(str)
df.yr = df.yr.astype(str)

group = df.groupby(('cyl', 'mfr'))

source = ColumnDataSource(group)
index_cmap = factor_cmap('cyl_mfr', palette=Spectral5, 
factors=sorted(df.cyl.unique()), end=1)

p = figure(plot_width=800, plot_height=300, title="Mean MPG by # Cylinders 
           and Manufacturer",
           x_range=group, toolbar_location=None, tools="")

p.vbar(x='cyl_mfr', top='mpg_mean', width=1, source=source,
       line_color="white", fill_color=index_cmap, )

p.y_range.start = 0
p.x_range.range_padding = 0.05
p.xgrid.grid_line_color = None
p.xaxis.axis_label = "Manufacturer grouped by # Cylinders"
p.xaxis.major_label_orientation = 1.2
p.outline_line_color = None

p.add_tools(HoverTool(tooltips=[("MPG", "@mpg_mean"), ("Cyl, Mfr", 
            "@cyl_mfr")]))

show(p)

Answer 1

group = df.groupby(('cyl', 'mfr'))成了<pandas.core.groupby.DataFrameGroupBy object at 0x0xxx>。如果你将它传递给ColumnDataSource，那么散景会有很多魔力，并且已经计算了很多统计数据

df.columns

Index(['mpg', 'cyl', 'displ', 'hp', 'weight', 'accel', 'yr', 'origin', 'name', 'mfr'],

source.column_names

[＆＃39; accel_count＆＃39;，＆＃39; accel_mean＆＃39;，＆＃39; accel_std＆＃39;，＆＃39; accel_min＆＃39;，＆＃39; accel_25％＆＃39;，＆＃39; accel_50％＆＃39;，＆＃39; accel_75％＆＃39;，＆＃39; accel_max＆＃39;，＆＃39; displ_count＆＃39; ，＆＃39; displ_mean＆＃39;，＆＃39; displ_std＆＃39;，＆＃39; displ_min＆＃39;，＆＃39; displ_25％＆＃39;，＆＃39; displ_50％＆＃39;，＆＃39; displ_75％＆＃39;，＆＃39; displ_max＆＃39;，＆＃39; hp_count＆＃39;，＆＃39; hp_mean＆＃39;，＆＃39; hp_std＆＃39;，＆＃39; hp_min＆＃39;，＆＃39; hp_25％＆＃39;，＆＃39; hp_50％＆＃39;，＆＃39; hp_75％＆＃39;，＆＃39; hp_max＆＃39; ，＆＃39; mpg_count＆＃39;，＆＃39; mpg_mean＆＃39;，＆＃39; mpg_std＆＃39;，＆＃39; mpg_min＆＃39;，＆＃39; mpg_25％＆＃39;，＆＃39; mpg_50％＆＃39;，＆＃39; mpg_75％＆＃39;，＆＃39; mpg_max＆＃39;，＆＃39; weight_count＆＃39;，＆＃39; weight_mean＆＃39;，＆＃39; weight_std＆＃39;，＆＃39; weight_min＆＃39;，＆＃39; weight_25％＆＃39;，＆＃39; weight_50％＆＃39;，＆＃39; weight_75％＆＃39;，＆＃39; weight_max＆＃39;，＆＃39; yr_count＆＃39;，＆＃39; yr_mean＆＃39;，＆＃39; yr_std＆＃39;，＆＃39; yr_min＆＃39;，＆＃39; yr_25％＆＃39;，＆＃39; yr_50％＆＃39;，＆＃39; yr_75％＆＃39;，＆＃39; yr_max＆＃39;，＆＃39; cyl_mfr＆＃39; ]

cyl_mfr是您按连接分组的2列的标签。在source中，这已成为元组列
mpg_sum未计算。如果你不能得到这笔钱，你需要自己计算一下。

如何使用bokeh vbar图表参数与groupby对象？

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