Removing connetion lines between missing Dates in ggplot

问题

I want to plot a time series with missing dates and values. Here is an example:

library(lubridate)
date_list = seq(ymd('1990-05-01'),ymd('2000-09-30'),by='day')
date_list = date_list[which(month(date_list) %in% c(5:9))]

value_list1 = sample(1:40, 1683, replace=TRUE)
value_list2 = sample(1:40, 1683, replace=TRUE)

testsample = data.frame(Date = date_list, Value1 = value_list1, Value2 = value_list2)

library(ggplot2)
ggplot(data = testsample, aes(x = Date)) +
  geom_line(aes(y = Value1), color = "black", size = 1, alpha=0.5) +
  geom_line(aes(y = Value2), color = "red", size = 1, alpha=0.5) +
  labs(subtitle="testplot", 
       x = "year", 
       y = "values") +
  scale_x_date(date_labels="%y",date_breaks  ="1 year")

I have no dates and data from November to April.

My plot looks like this:

How can I remove those connection lines between the years? I read about transforming the dates into factors, but I am not sure about this. Is there another solution?

回答1:

One solution would be to specify the group aesthetics to match the groups you want to have connected by lines.

In your case this is the year:

ggplot(data = testsample, aes(x = Date, group = year(Date))) +
  geom_line(aes(y = Value1), color = "black", size = 1, alpha=0.5) +
  geom_line(aes(y = Value2), color = "red", size = 1, alpha=0.5) +
  labs(subtitle="testplot", 
       x = "year", 
       y = "values") +
  scale_x_date(date_labels = "%y", date_breaks  ="1 year")

Building on Gregors comment we can also change implicit missing values to explicit missing values, e.g. using tidyr::complete:

testsample2 <- tidyr::complete(testsample, Date = seq(min(Date), max(Date), by = "day"))
ggplot(data = testsample2, aes(x = Date)) +
  geom_line(aes(y = Value1), color = "black", size = 1, alpha=0.5) +
  geom_line(aes(y = Value2), color = "red", size = 1, alpha=0.5) +
  labs(subtitle="testplot", 
       x = "year", 
       y = "values") +
  scale_x_date(date_labels = "%y", date_breaks  ="1 year")

来源：https://stackoverflow.com/questions/56425915/removing-connetion-lines-between-missing-dates-in-ggplot

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