R: Append column with count for a specific value

Question

I'm looking for an easy way to subset my df and append a column with a frequency count. Suppose I have a df like this:

Name  
JA
JN
JA
JB
JA
JN

And I want to have an outcome like this:

 Name    Frequency 
    JA      3
    JN      2
    JB      1

Any suggestion? Thank you.

What have you tried? It might include `split`, `by`, or `dplyr::group_by` with `dplyr::summarize`. — r2evans, Aug 08 '16 at 16:45
This can solve your problem http://stackoverflow.com/questions/18799901/data-frame-group-by-column — Erick Díaz, Aug 08 '16 at 16:48

score 1 · Accepted Answer · answered Aug 08 '16 at 16:47

1

We can use tally after grouping by 'Name' with dplyr

library(dplyr)
df1 %>% 
  group_by(Name) %>%
  tally()

Or use table from base R

as.data.frame(table(df1[,1]))
#   Var1 Freq
#1   JA    3
#2   JB    1
#3   JN    2

answered Aug 08 '16 at 16:47

akrun

score 0 · Answer 2 · answered Aug 08 '16 at 16:51

0

One way to do it using data.table.

require(data.table)
DT<-data.table(df)
DT[,.(Frequency=.N),by=Name]

answered Aug 08 '16 at 16:51

Vamsi Prabhala

you could shorten the code to a more efficient way: `setDT(df)[,.(Freq=.N), by=Name]` – Sathish Aug 08 '16 at 16:56

2 Answers2