Compare frequencies of samples in r

问题

I would like to compare the frequency of samples from two different observations. The problem is that the first doesn't contain the whole range of numbers of the second. How could I combine these without writing a for loop sorting them based on the x values returned by count? Here's a MWE for clarification:

library(plyr)
a <- c(5, 4, 5, 7, 3, 5, 6, 5, 5, 4, 5, 5, 4, 5, 4, 7, 2, 4, 4, 5, 3, 6, 5, 6, 4, 4, 5, 4, 5, 5, 6, 7, 4)
b <- c(1, 3, 4, 6, 2, 7, 7, 4, 3, 6, 6, 3, 6, 6, 5, 6, 6, 5)

a.count <- count(a)
b.count <- count(b)

My desired result should look somehow like that:

   freq.a freq.b                   
1  1         
2  1       1                                       
3  3       2   
4  2      10                                              
5  2      13
6  7       4                                            
7  2       3

回答1:

df <- merge(a.count, b.count, by ='x', all=TRUE)[2:3]
names(df) <- c('freq.a', 'freq.b')
df

  freq.a freq.b
1     NA      1
2      1      1
3      2      3
4     10      2
5     13      2
6      4      7
7      3      2

回答2:

If you put your data in long format (one row per observation, with a variable for which sample it is from), then you can just make a contingency table:

    data.frame(v=df.a, s='a') %>% rbind(data.frame(v=df.b, s='b')) %>%
      xtabs(f=~v+s)

Produces:

   s
v    a  b
  1  0  1
  2  1  1
  3  2  3
  4 10  2
  5 13  2
  6  4  7
  7  3  2

来源：https://stackoverflow.com/questions/40792432/compare-frequencies-of-samples-in-r