CODEWITHSUNDEEP
rdataframe
887
887

Reputation: 619

How to create column that indicates number of times that an ID appear?

I'm looking to create a column that indicates, for every unique value, the number of times that it appears in a data set. I would like to generate the frequency column in the data frame below:

ID     Frequency
111       4
205       2
603       6
111       4

In the original data, 111 appeared 4 times, 205 appeared 2 times, and 603 appeared 6 times, etc.

Upvotes: 0

Views: 566

Answers (3)

Duck
Duck

Reputation: 39613

Based on @rogues77 comments, and after having given the approach initially, the solution can be:

library(dplyr)
#Code 1
newdf <- df %>% group_by(ID) %>% mutate(N=n())
#Code 2
newdf <- df %>% group_by(ID) %>% summarise(N=n())

Upvotes: 2

akrun
akrun

Reputation: 887971

We can also use data.table methods

library(data.table)
setDT(DF)[, Freq := .N, ID]

data

DF <- structure(list(ID = c(111L, 205L, 603L, 111L)), class = "data.frame", 
    row.names = c(NA, 
-4L))

Upvotes: 1

G. Grothendieck
G. Grothendieck

Reputation: 270378

With the input data DF shown reproducibly in the Note at the end, use ave with length. No packages are used.

nr <- nrow(DF)
transform(DF, Freq = ave(1:nr, ID, FUN = length))

giving:

   ID Freq
1 111    2
2 205    1
3 603    1
4 111    2

or with dplyr

library(dplyr)
DF %>%
  group_by(ID) %>%
  mutate(Freq = n()) %>%
  ungroup

Note

Lines <- "ID
111       
205       
603       
111       "
DF <- read.table(text = Lines, header = TRUE)

Upvotes: 2

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