R Error in unique.default(x, nmax = nmax) : unique() applies only to vectors (2 Examples)

In this article, I’ll show how to reproduce and fix the “Error in unique.default(x, nmax = nmax) : unique() applies only to vectors” in the R programming language.

Creation of Example Data

data(iris)                    # Load example data
head(iris)
#   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1          5.1         3.5          1.4         0.2  setosa
# 2          4.9         3.0          1.4         0.2  setosa
# 3          4.7         3.2          1.3         0.2  setosa
# 4          4.6         3.1          1.5         0.2  setosa
# 5          5.0         3.6          1.4         0.2  setosa
# 6          5.4         3.9          1.7         0.4  setosa

Example 1: Replicating the Error Message in unique.default(x, nmax = nmax) : unique() applies only to vectors

ave(iris$Sepal.Length,        # Trying to use mean without FUN =
    iris$Species,
    mean)
# Error in unique.default(x, nmax = nmax) : 
#   unique() applies only to vectors

Example 2: Solving the Error Message in unique.default(x, nmax = nmax) : unique() applies only to vectors

ave(iris$Sepal.Length,        # Specifying FUN =
    iris$Species,
    FUN = mean)
#   [1] 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006
#  [13] 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006
#  [25] 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006
#  [37] 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006 5.006
#  [49] 5.006 5.006 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936
#  [61] 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936
#  [73] 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936
#  [85] 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936 5.936
#  [97] 5.936 5.936 5.936 5.936 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588
# [109] 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588
# [121] 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588
# [133] 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588 6.588
# [145] 6.588 6.588 6.588 6.588 6.588 6.588

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