# How to find the percentage of each category in a data.table object column in R?

To find the percentage of each category in a data.table object in R, we can follow the below steps −

• First of all, create a data.table object.

• Then, use summarise function of dplyr package after grouping along with n and nrow.

## Example

#### Create the data.table object

Let’s create a data.table object as shown below −

library(data.table)
Factor<-sample(c("very low","low","medium","high","very high"),25,replace=TRUE)
Response<-rnorm(25)
DT<-data.table(Factor,Response)
DT

## Output

On executing, the above script generates the below output(this output will vary on your system due to randomization) −

    Factor     Response
1:  low       -1.61215323
2:  very high -0.44482842
3:  very low  -0.08886876
4:  very high -0.23859749
5:  high       0.24527395
6:  low        1.36309052
7:  low        0.85434533
8:  low       -0.04598830
9:  high      -0.09693464
10: low       -0.66470019
11: high      -0.27726887
12: medium     0.30070368
13: very low  -1.10935270
14: high       2.05570820
15: low       -0.61390253
16: low        1.04354500
17: high      -1.74834030
18: very low  -0.84208037
19: medium     2.26732484
20: very high -0.30309612
21: low        0.72720852
22: high      -2.52034038
23: very low -1.50381843
24: high     -0.61927487
25: high      0.14854389
Factor      Response

Find the percentage of each category in data.table object

Using summarise function of dplyr package after grouping along with n and nrow to find the percentage of each category in Factor column of data.table object DT −

library(data.table)
Factor<-sample(c("very low","low","medium","high","very high"),25,replace=TRUE)
Response<-rnorm(25)
DT<-data.table(Factor,Response)
library(dplyr)
DT %>% group_by(Factor) %>% summarise(Percent=n()/nrow(.))

## Output

# A tibble: 5 x 2
Factor  Percent
<chr>     <dbl>
1 high      0.32
2 low       0.32
3 medium    0.08
4 very high 0.12
5 very low  0.16