R直方图。 如何标记一些而非全部数据点

Question

My dataframe contains three variables:

Row_Number    Sample_ID    Expression_Level
1             hum_449      0.25
2             hum_459      0.35
4             mur_223      0.45

I want to produce histograms of the third column using

hist(dataframe$Expression_Level)

And I want to label some of the bars with a list a list of Sample_ID values that correspond to that particular expression level.

I have the desired Sample_IDs stored as a list object and also as a data frame with corresponding Row_Number and Expression_Level values (essentially just a subset of the original data frame). I don't know what to do next or even what to type into a search engine.

I have ggplot2 installed because friends told me it would probably be helpful but I am unfamiliar with it and face the same problem of not knowing what to look for when reading the documentation. Would prefer not to install more packages if possible.

Answer 1

You could use the following to add a label corresponding to the third element of Sample_ID to the third "bar" of a histogram. But, this seems like an odd way to go really, since the bars of a histogram are counts. Might you be wanting to use barplot instead? same code would work with "barplot" instead of hist.

temp <- hist(dataframe$Expression_Level) mtext(text=Expression_Level[3],side=1,line=2,at=temp[3])

Answer 2

Something like this?

set.seed(1)      # for reproduceale example
# crate sample data - you have this already
df <- data.frame(sample_ID=paste0("S-",1:100),
                 Expression_Level=round(runif(100),1),
                 stringsAsFactors=F)

# you start here...
labels     <- aggregate(sample_ID~Expression_Level,df,c)
labels$lab <- sapply(labels$sample_ID,function(x)paste(unlist(x),collapse="|"))

library(ggplot2)
ggplot(df, aes(x=factor(Expression_Level))) + 
  geom_histogram(fill="lightgreen",color="grey50")+
  geom_text(data=labels,aes(y=.1,label=lab),hjust=0)+
  labs(x="Expression_Level")+
  coord_flip()