library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
library(reprex)
rm (list = ls())

a <- c("dog", "cat", "dog", "camel", "dog", "cat", "dog")
b <- c(1,0,1,1,1,0,1)
x <- data.frame(a,b)
x
#>       a b
#> 1   dog 1
#> 2   cat 0
#> 3   dog 1
#> 4 camel 1
#> 5   dog 1
#> 6   cat 0
#> 7   dog 1
attach(x)
#> The following objects are masked _by_ .GlobalEnv:
#> 
#>     a, b
#y <- summarise(group_by(x,a), sum(b))
#y
#x
x %>% group_by(a) %>% summarise(sum_animal = sum(b))
#> # A tibble: 3 x 2
#>   a     sum_animal
#>   <fct>      <dbl>
#> 1 camel          1
#> 2 cat            0
#> 3 dog            4

x$c <- x %>% group_by(a) %>% summarise(sum_animal = sum(b))
#> Error in `$<-.data.frame`(`*tmp*`, c, value = structure(list(a = structure(1:3, .Label = c("camel", : replacement has 3 rows, data has 7

#Would like to create a new vector c in dataframe x which would have the values of  the total frequency of an animal
#in vector b for every value (animal name) in vector a. So c should have the values 4,0,4, 1,4,0, 4

^{Created on 2019-08-31 by the reprex package (v0.2.1)}