if else 条件在 ggplot 添加一个额外的层 [英] if else condition in ggplot to add an extra layer

问题描述

假设我想在 ggplot 中绘制两个图层，一个包含点，另一个包含满足特定条件的线.

没有条件的代码可能如下所示:

library("ggplot2")# 按电影年份汇总电影评分数量mry <- do.call(rbind, by(movies, round(movies$rating), function(df) {nums <- tapply(df$length,df$year,length)data.frame(rating=round(df$rating[1]), year = as.numeric(names(nums)), number=as.vector(nums))}))p <- ggplot(mry, aes(x=year, y=number, group=rating))p +geom_point()+geom_line()

现在绘制点而不仅仅是线的条件是，名为 tmp.data 的对象不等于表达式无值".

tmp.data<-c(1,2,3) # 在这种情况下条件满足# 尝试绘制两个图层，包括绘图函数中的条件p+if(tmp.data[1]!="no value"){ geom_point()+}geom_line()

失败....

错误:意外的}"在:"p+if(tmp.data[1]!="no value"){ geom_point()+}"

<块引用>

geom_line()geom_line:
stat_identity:
位置标识:(宽度= NULL，高度= NULL)

解决方案

您看到的是语法错误.我能想到的最可靠的方法是:

tmp.data<-c(1,2,3)if(tmp.data[1]!="无值") {p = p + geom_point()}p + geom_line()

所以你将对象 p 组合成一个序列，只在 if 语句产生 TRUE 时添加 geom_point().

say I want to plot two layers in ggplot, one containing points and another one containing lines if a certain criteria is fulfilled.

The code without the criteria could look like this:

library("ggplot2")

# Summarise number of movie ratings by year of movie
mry <- do.call(rbind, by(movies, round(movies$rating), function(df) {
  nums <- tapply(df$length, df$year, length)
  data.frame(rating=round(df$rating[1]), year = as.numeric(names(nums)), number=as.vector(nums))
}))

p <- ggplot(mry, aes(x=year, y=number, group=rating))

p + 
geom_point()+
geom_line()

now the condition for plotting the points and not only the lines would be, that an object called tmp.data does not equal the expression "no value".

tmp.data<-c(1,2,3) # in this case the condition is fulfilled

# attempt to plot the two layers including the condition in the plotting function
p+ 
  if(tmp.data[1]!="no value"){ geom_point()+}
  geom_line()

fails....

Error: unexpected '}' in:
"p+ 
if(tmp.data[1]!="no value"){ geom_point()+}"

geom_line() geom_line:
stat_identity:
position_identity: (width = NULL, height = NULL)

解决方案

What you are seeing is a syntax error. The most robust way I can think of is:

tmp.data<-c(1,2,3) 
if(tmp.data[1]!="no value") {
   p = p + geom_point()
}
p + geom_line()

So you compose the object p in a sequence, only adding geom_point() when the if statements yields TRUE.

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