子集观察（行）
dplyr::filter() - 选择符合逻辑条件的数据框中的行子集：
dplyr::filter(iris,Sepal.Length>7)
# Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1 7.1 3.0 5.9 2.1 virginica
# 2 7.6 3.0 6.6 2.1 virginica
# 3 7.3 2.9 6.3 1.8 virginica
# 4 7.2 3.6 6.1 2.5 virginica
# 5 7.7 3.8 6.7 2.2 virginica
# 6 7.7 2.6 6.9 2.3 virginica
# 7 7.7 2.8 6.7 2.0 virginica
# 8 7.2 3.2 6.0 1.8 virginica
# 9 7.2 3.0 5.8 1.6 virginica
# 10 7.4 2.8 6.1 1.9 virginica
# 11 7.9 3.8 6.4 2.0 virginica
# 12 7.7 3.0 6.1 2.3 virginica
dplyr::distinct() - 删除重复的行：
distinct(iris, Sepal.Length, .keep_all = TRUE)
# 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
# 7 4.4 2.9 1.4 0.2 setosa
# 8 4.8 3.4 1.6 0.2 setosa
# 9 4.3 3.0 1.1 0.1 setosa
# 10 5.8 4.0 1.2 0.2 setosa
# 11 5.7 4.4 1.5 0.4 setosa
# 12 5.2 3.5 1.5 0.2 setosa
# 13 5.5 4.2 1.4 0.2 setosa
# 14 4.5 2.3 1.3 0.3 setosa
# 15 5.3 3.7 1.5 0.2 setosa
# 16 7.0 3.2 4.7 1.4 versicolor
# 17 6.4 3.2 4.5 1.5 versicolor
# 18 6.9 3.1 4.9 1.5 versicolor
# 19 6.5 2.8 4.6 1.5 versicolor
# 20 6.3 3.3 4.7 1.6 versicolor
# 21 6.6 2.9 4.6 1.3 versicolor
# 22 5.9 3.0 4.2 1.5 versicolor
# 23 6.0 2.2 4.0 1.0 versicolor
# 24 6.1 2.9 4.7 1.4 versicolor
# 25 5.6 2.9 3.6 1.3 versicolor
# 26 6.7 3.1 4.4 1.4 versicolor
# 27 6.2 2.2 4.5 1.5 versicolor
# 28 6.8 2.8 4.8 1.4 versicolor
# 29 7.1 3.0 5.9 2.1 virginica
# 30 7.6 3.0 6.6 2.1 virginica
# 31 7.3 2.9 6.3 1.8 virginica
# 32 7.2 3.6 6.1 2.5 virginica
# 33 7.7 3.8 6.7 2.2 virginica
# 34 7.4 2.8 6.1 1.9 virginica
# 35 7.9 3.8 6.4 2.0 virginica