R count number of Team members based on Team name - r

Question

I have a df where each row represents an individual and each column a characteristic of these individuals. One of the columns is TeamName, which is the name of the Team that individual belongs to. Multiple individuals belong to a Team.
I'd like a function in R that creates a new column with the number of team members for each Team.
So, for example I have:
df
Name Surname TeamName
John Smith Champions
Mary Osborne Socceroos
Mark Johnson Champions
Rory Bradon Champions
Jane Bryant Socceroos
Bruce Harper
I'd like to have
df1
Name Surname TeamName TeamNo
John Smith Champions 3
Mary Osborne Socceroos 2
Mark Johnson Champions 3
Rory Bradon Champions 3
Jane Bryant Socceroos 2
Bruce Harper 0
So as you can see the counting includes that individual too, and if someone (e.g. Bruce Harper) has no Team name, then he gets a 0.
How can I do that? Thanks!

Answer 1

This is a solution based on using data.table which perhaps is too much for what you need, but here it goes:
library(data.table)
dt=data.table(df)
# First, let's convert the factors of TeamName, to characters
dt[,TeamName:=as.character(TeamName)]
# Now, let find all the team numbers
dt[,TeamNo:=.N, by='TeamName']
# Let's exclude the special cases
dt[is.na(TeamName),TeamNo:=NA]
dt[TeamName=="",TeamNo:=NA]
It is clearly not the best solution, but I hope this helps

Answer 2

If you need to know the number of unique members in the first two columns based on the 'TeamName' column, one option is n_distinct from dplyr
library(dplyr)
library(tidyr)
df %>%
unite(Var, Name, Surname) %>% #paste the columns together
group_by(TeamName) %>% #group by TeamName
mutate(TeamNo= n_distinct(Var)) %>% #create the TeamNo column
separate(Var, into=c('Name', 'Surname')) #split the 'Var' column
Or if it just the number of rows per 'TeamName', we can group by 'TeamName', get the number of rows per group with n(), create the 'TeamNo' column with mutate based on that n(), and if needed an ifelse condition can be used to give NA for 'TeamName' that are '' or NA.
df %>%
group_by(TeamName) %>%
mutate(TeamNo = ifelse(is.na(TeamName)|TeamName=='', NA_integer_, n()))
# Name Surname TeamName TeamNo
#1 John Smith Champions 3
#2 Mary Osborne Socceroos 2
#3 Mark Johnson Champions 3
#4 Rory Bradon Champions 3
#5 Jane Bryant Socceroos 2
#6 Bruce Harper NA
Or you can use ave from base R. Suppose if there are '' and NA, I would first convert the '' to NA and then use ave to get the length of 'TeamNo' grouped by that column. It will give NA for `NA' values. For example.
v1 <- c(df$TeamName, NA)# appending an NA with the example to show the case
is.na(v1) <- v1=='' #convert the `'' to `NA`
as.numeric(ave(v1, v1, FUN=length))
#[1] 3 2 3 3 2 NA NA

Answer 3

Using sqldf:
library(sqldf)
sqldf("SELECT Name, Surname, TeamName, n
FROM df
LEFT JOIN
(SELECT TeamName, COUNT(Name) AS n
FROM df
WHERE NOT TeamName IS '' GROUP BY TeamName)
USING (TeamName)")
Output:
Name Surname TeamName n
1 John Smith Champions 3
2 Mary Osborne Socceroos 2
3 Mark Johnson Champions 3
4 Rory Bradon Champions 3
5 Jane Bryant Socceroos 2
6 Bruce Harper NA