Examine whether group members make the same choices

A MWE.

df <- tibble(ID = c(1:12),
             Group = c(rep(1,3), rep(2,3), rep(3,3), rep(4,3)),
             Choice = c( rep(1.5, 3), round(rnorm(n=9,mean=10,sd=5), digits = 1) )
             )

What I want is to identify, in each group, whether the group members decisions are the same or not. The desired output should be something like:

df <- tibble(ID = c(1:12),
             Group = c(rep(1,3), rep(2,3), rep(3,3), rep(4,3)),
             Choice = c( rep(1.5, 3), round(rnorm(n=9,mean=10,sd=5), digits = 1) )，
             Symmetric = c ( rep(1, 3), rep(0, 9) )
             )

Is there a fast and simple solution for this? Thanks a lot!

Couple of ideas -

1. You may count the unique values per group.

library(dplyr)

df %>% mutate(Symmetric = as.integer(n_distinct(Choice) == 1), .by = Group)

In base R :

transform(df, Symmetric = as.integer(ave(Choice, Group, FUN = \(x) length(unique(x)) == 1)))

2. since Choice is a numeric value we can also check it's standard deviation sd

df %>% mutate(Symmetric = as.integer(sd(Choice) == 0), .by = Group)

In base R :

transform(df, Symmetric = as.integer(ave(Choice, Group, FUN = sd) == 0))

All of which return :

#   ID Group Choice Symmetric
#1   1     1    1.5         1
#2   2     1    1.5         1
#3   3     1    1.5         1
#4   4     2    9.7         0
#5   5     2   -0.2         0
#6   6     2   12.9         0
#7   7     3   23.7         0
#8   8     3    2.3         0
#9   9     3   12.5         0
#10 10     4    7.5         0
#11 11     4    2.0         0
#12 12     4   14.0         0