The goal of this tutorial is to learn how to use the grep function. A function very useful to find patterns in texts.
# In this tutorial we are going to use the iris dataset
# We will count the amount of plants of each Species
data("iris")
iris$Species <- as.character(iris$Species)
str(iris)## 'data.frame': 150 obs. of 5 variables:
## $ Sepal.Length: num 5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
## $ Sepal.Width : num 3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...
## $ Petal.Length: num 1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
## $ Petal.Width : num 0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
## $ Species : chr "setosa" "setosa" "setosa" "setosa" ...# The grep function finds the position where the pattern is found
grep("setosa", iris$Species)## [1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
## [24] 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
## [47] 47 48 49 50# The great power of this function is that we can match partial patterns
grep("set", iris$Species)## [1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
## [24] 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
## [47] 47 48 49 50# However, we could find problems like case sensitive patterns
grep("Setosa", iris$Species)## integer(0)# We can skip this problem using the ignore.case parameter
grep("Setosa", iris$Species, ignore.case = TRUE)## [1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
## [24] 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
## [47] 47 48 49 50# We can as well find the positions where the pattern is NOT found using invert
grep("Setosa", iris$Species, ignore.case = TRUE, invert = TRUE)## [1] 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67
## [18] 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84
## [35] 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101
## [52] 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118
## [69] 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135
## [86] 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150In this tutorial we have learnt how to find patterns in data using the grep function.