R提取频率

Question

I am trying to get the frequencies but my ids are repeating. Here is a sample data:

id <- c(1,1,2,2,3,3)
gender <- c("m","m","f","f","m","m")
score <- c(10,5,10,5,10,5)
data <- data.frame("id"=id,"gender"=gender, "score"=score)

> data
  id gender score
1  1      m    10
2  1      m     5
3  2      f    10
4  2      f     5
5  3      m    10
6  3      m     5

I would like to get the frequencies of the gender categories but I have repeating ids. When I run this code below:

gender<-as.data.frame(table(data$gender))
> gender
  Var1 Freq
1    f    2
2    m    4

The frequency should be female = 1, male =2. it should look like this below:

> gender
  Var1 Freq
1    f    1
2    m    2

How can I get this considering the id information?

Answer 1

You can use data.table::uniqueN to count the number of unique ids per gender group

library(data.table)
setDT(data)

data[, .(Freq = uniqueN(id)), gender]

#    gender Freq
# 1:      m    2
# 2:      f    1

Answer 2

The idea from @IceCreamToucan with dplyr :

data %>%
 group_by(gender) %>%
 summarise(freq = n_distinct(id))

  gender  freq
  <fct>  <int>
1 f          1
2 m          2

Answer 3

In base R

rowSums(table(data$gender,data$id)!=0)
f m 
1 2 

Answer 4

Being late to the party, I was quite surprised about the sophisticated answers which use grouping or rowSums() .

In base R, I would

1. remove the duplicate id rows from the data.frame by subsetting with duplicated(id) ,
2. apply table() on the gender column.

So, the code is

table(data[duplicated(data$id), "gender"])

 fm 1 2