Analogous function for count and add_count in dplyr.
count(.data, ..., sort = FALSE, name = "n")
add_count(.data, ..., name = "n")data.table
a = as.data.table(mtcars)
count(a,cyl)
#> cyl n
#> <num> <int>
#> 1: 6 7
#> 2: 4 11
#> 3: 8 14
count(a,cyl,sort = TRUE)
#> cyl n
#> <num> <int>
#> 1: 8 14
#> 2: 4 11
#> 3: 6 7
a
#> mpg cyl disp hp drat wt qsec vs am gear carb
#> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num>
#> 1: 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
#> 2: 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
#> 3: 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
#> 4: 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
#> 5: 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
#> 6: 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
#> 7: 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
#> 8: 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
#> 9: 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
#> 10: 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
#> 11: 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
#> 12: 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3
#> 13: 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3
#> 14: 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3
#> 15: 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4
#> 16: 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4
#> 17: 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4
#> 18: 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
#> 19: 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
#> 20: 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
#> 21: 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
#> 22: 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2
#> 23: 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2
#> 24: 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4
#> 25: 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2
#> 26: 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
#> 27: 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
#> 28: 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
#> 29: 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4
#> 30: 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
#> 31: 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8
#> 32: 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
#> mpg cyl disp hp drat wt qsec vs am gear carb
b = as.data.table(iris)
b %>% add_count(Species,name = "N")
#> Sepal.Length Sepal.Width Petal.Length Petal.Width Species N
#> <num> <num> <num> <num> <fctr> <int>
#> 1: 5.1 3.5 1.4 0.2 setosa 50
#> 2: 4.9 3.0 1.4 0.2 setosa 50
#> 3: 4.7 3.2 1.3 0.2 setosa 50
#> 4: 4.6 3.1 1.5 0.2 setosa 50
#> 5: 5.0 3.6 1.4 0.2 setosa 50
#> ---
#> 146: 6.7 3.0 5.2 2.3 virginica 50
#> 147: 6.3 2.5 5.0 1.9 virginica 50
#> 148: 6.5 3.0 5.2 2.0 virginica 50
#> 149: 6.2 3.4 5.4 2.3 virginica 50
#> 150: 5.9 3.0 5.1 1.8 virginica 50
b
#> Sepal.Length Sepal.Width Petal.Length Petal.Width Species N
#> <num> <num> <num> <num> <fctr> <int>
#> 1: 5.1 3.5 1.4 0.2 setosa 50
#> 2: 4.9 3.0 1.4 0.2 setosa 50
#> 3: 4.7 3.2 1.3 0.2 setosa 50
#> 4: 4.6 3.1 1.5 0.2 setosa 50
#> 5: 5.0 3.6 1.4 0.2 setosa 50
#> ---
#> 146: 6.7 3.0 5.2 2.3 virginica 50
#> 147: 6.3 2.5 5.0 1.9 virginica 50
#> 148: 6.5 3.0 5.2 2.0 virginica 50
#> 149: 6.2 3.4 5.4 2.3 virginica 50
#> 150: 5.9 3.0 5.1 1.8 virginica 50