散景流问题：转移线

Question

我有以下代码：

import random
import datetime as dt

from bokeh.models import ColumnDataSource
from bokeh.plotting import curdoc, figure


source = ColumnDataSource(dict(
    x = [], y = []
))

p = figure(plot_height=250, plot_width=400, tools="save",
           x_axis_type="datetime", y_axis_location="right")
p.x_range.follow = "end"
p.x_range.follow_interval = 5000  # ms
p.line(x='x', y='y', color='red', source=source)

cur_time = dt.datetime.now()
step = dt.timedelta(seconds=1)

def update():
    global cur_time, step
    new_data = dict(x=[], y=[])
    new_data['x'].append(cur_time)
    new_data['y'].append(random.randint(1, 100))
    cur_time += step
    source.stream(new_data, 60)  # how many data are saved

curdoc().add_root(p)
curdoc().add_periodic_callback(update, 500)

我想剪切数据，因此我将翻转参数添加到stream method。起初可以：

但过了一会儿，这条线开始转移：

为什么会这样？以及如何解决这个问题？

感谢您的帮助！

Answer 1

import random
import datetime as dt

from bokeh.models import ColumnDataSource
from bokeh.plotting import curdoc, figure


source = ColumnDataSource(dict(
    x = [], y = []
))

p = figure(plot_height=250, plot_width=400, tools="save",
           x_axis_type="datetime", y_axis_location="right")
# p.x_range.follow = "end" #***** THIS IS YOUR ISSUE *****
p.x_range.follow_interval = 500  # ms
p.line(x='x', y='y', color='red', source=source)

cur_time = dt.datetime.now()
step = dt.timedelta(seconds=1)

def update():
    global cur_time, step
    new_data = dict(x=[], y=[])
    new_data['x'].append(cur_time)
    new_data['y'].append(random.randint(1, 100))
    cur_time += step
    source.stream(new_data, 60)  # how many data are saved

curdoc().add_root(p)
curdoc().add_periodic_callback(update, 50)

查看我的编辑。不需要x_range.follow，请参阅http://bokeh.pydata.org/en/0.11.1/docs/reference/models/ranges.html