How to find out the unique elements in a vector
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Say there are 100 students being graded
# Prepare some sample grades. > grades = round(rnorm(100,mean=3.5,sd=0.5),1) > grades [1] 4.0 4.2 2.9 3.6 3.5 3.5 3.6 4.2 3.6 3.2 4.0 3.8 2.8 4.2 [15] 3.2 4.1 3.8 3.4 3.1 4.2 3.5 2.8 3.5 4.2 3.2 3.0 3.2 3.4 [29] 3.9 3.2 3.8 3.2 3.3 3.5 3.8 4.0 3.2 3.5 2.7 3.5 3.1 3.3 [43] 3.8 3.9 4.0 3.8 4.7 2.9 2.6 3.8 4.1 3.1 3.7 4.1 3.7 2.4 [57] 3.6 2.4 2.8 3.3 3.2 2.9 3.3 3.1 4.0 3.3 3.4 3.5 3.8 4.2 [71] 3.4 3.3 2.3 3.5 3.5 4.1 4.2 3.7 4.3 2.7 3.7 4.5 3.2 3.3 [85] 3.3 3.0 3.5 2.5 3.8 3.1 4.4 2.7 3.3 3.7 3.4 3.5 4.1 4.2 [99] 3.7 4.2
and you want to find out how many unique grades there are.
UNIQUE () function
> unique(grades) [1] 4.0 4.2 2.9 3.6 3.5 3.2 3.8 2.8 4.1 3.4 3.1 3.0 3.9 3.3 2.7 [16] 4.7 2.6 3.7 2.4 2.3 4.3 4.5 2.5 4.4
TABLE () function
> table(grades) grades 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5 4.7 1 2 1 1 3 3 3 2 5 9 9 5 12 4 6 9 2 5 5 9 1 1 1 1