# Iteration

Time Estimates:
Â Â Â Â  Videos: 30 min
Â Â Â Â  Readings: 0 min
Â Â Â Â  Activities: 60 min
Â Â Â Â  Check-ins: 2

Required Video: Functional Programming

Required Tutorial: Iteration

Check-In 1: Functional Programming

Recall that in the last unit, we discussed the challenge of standardizing many columns in a data frame. For example, we wanted to standardize all the numeric variables in the dataset iris.

Here is the function we wrote for that:

standardize <- function(data) {
deviations <- data - mean(data, na.rm = TRUE)
newdata <- deviations / sd(data, na.rm = TRUE)
return(newdata)
}

Question 1: Why does the following not work?

iris %>%
mutate(
Petal.Length = map_dbl(Petal.Length, standardize)
)
##     Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
## 1            5.1         3.5           NA         0.2     setosa
## 2            4.9         3.0           NA         0.2     setosa
## 3            4.7         3.2           NA         0.2     setosa
## 4            4.6         3.1           NA         0.2     setosa
## 5            5.0         3.6           NA         0.2     setosa
## 6            5.4         3.9           NA         0.4     setosa
## 7            4.6         3.4           NA         0.3     setosa
## 8            5.0         3.4           NA         0.2     setosa
## 9            4.4         2.9           NA         0.2     setosa
## 10           4.9         3.1           NA         0.1     setosa
## 11           5.4         3.7           NA         0.2     setosa
## 12           4.8         3.4           NA         0.2     setosa
## 13           4.8         3.0           NA         0.1     setosa
## 14           4.3         3.0           NA         0.1     setosa
## 15           5.8         4.0           NA         0.2     setosa
## 16           5.7         4.4           NA         0.4     setosa
## 17           5.4         3.9           NA         0.4     setosa
## 18           5.1         3.5           NA         0.3     setosa
## 19           5.7         3.8           NA         0.3     setosa
## 20           5.1         3.8           NA         0.3     setosa
## 21           5.4         3.4           NA         0.2     setosa
## 22           5.1         3.7           NA         0.4     setosa
## 23           4.6         3.6           NA         0.2     setosa
## 24           5.1         3.3           NA         0.5     setosa
## 25           4.8         3.4           NA         0.2     setosa
## 26           5.0         3.0           NA         0.2     setosa
## 27           5.0         3.4           NA         0.4     setosa
## 28           5.2         3.5           NA         0.2     setosa
## 29           5.2         3.4           NA         0.2     setosa
## 30           4.7         3.2           NA         0.2     setosa
## 31           4.8         3.1           NA         0.2     setosa
## 32           5.4         3.4           NA         0.4     setosa
## 33           5.2         4.1           NA         0.1     setosa
## 34           5.5         4.2           NA         0.2     setosa
## 35           4.9         3.1           NA         0.2     setosa
## 36           5.0         3.2           NA         0.2     setosa
## 37           5.5         3.5           NA         0.2     setosa
## 38           4.9         3.6           NA         0.1     setosa
## 39           4.4         3.0           NA         0.2     setosa
## 40           5.1         3.4           NA         0.2     setosa
## 41           5.0         3.5           NA         0.3     setosa
## 42           4.5         2.3           NA         0.3     setosa
## 43           4.4         3.2           NA         0.2     setosa
## 44           5.0         3.5           NA         0.6     setosa
## 45           5.1         3.8           NA         0.4     setosa
## 46           4.8         3.0           NA         0.3     setosa
## 47           5.1         3.8           NA         0.2     setosa
## 48           4.6         3.2           NA         0.2     setosa
## 49           5.3         3.7           NA         0.2     setosa
## 50           5.0         3.3           NA         0.2     setosa
## 51           7.0         3.2           NA         1.4 versicolor
## 52           6.4         3.2           NA         1.5 versicolor
## 53           6.9         3.1           NA         1.5 versicolor
## 54           5.5         2.3           NA         1.3 versicolor
## 55           6.5         2.8           NA         1.5 versicolor
## 56           5.7         2.8           NA         1.3 versicolor
## 57           6.3         3.3           NA         1.6 versicolor
## 58           4.9         2.4           NA         1.0 versicolor
## 59           6.6         2.9           NA         1.3 versicolor
## 60           5.2         2.7           NA         1.4 versicolor
## 61           5.0         2.0           NA         1.0 versicolor
## 62           5.9         3.0           NA         1.5 versicolor
## 63           6.0         2.2           NA         1.0 versicolor
## 64           6.1         2.9           NA         1.4 versicolor
## 65           5.6         2.9           NA         1.3 versicolor
## 66           6.7         3.1           NA         1.4 versicolor
## 67           5.6         3.0           NA         1.5 versicolor
## 68           5.8         2.7           NA         1.0 versicolor
## 69           6.2         2.2           NA         1.5 versicolor
## 70           5.6         2.5           NA         1.1 versicolor
## 71           5.9         3.2           NA         1.8 versicolor
## 72           6.1         2.8           NA         1.3 versicolor
## 73           6.3         2.5           NA         1.5 versicolor
## 74           6.1         2.8           NA         1.2 versicolor
## 75           6.4         2.9           NA         1.3 versicolor
## 76           6.6         3.0           NA         1.4 versicolor
## 77           6.8         2.8           NA         1.4 versicolor
## 78           6.7         3.0           NA         1.7 versicolor
## 79           6.0         2.9           NA         1.5 versicolor
## 80           5.7         2.6           NA         1.0 versicolor
## 81           5.5         2.4           NA         1.1 versicolor
## 82           5.5         2.4           NA         1.0 versicolor
## 83           5.8         2.7           NA         1.2 versicolor
## 84           6.0         2.7           NA         1.6 versicolor
## 85           5.4         3.0           NA         1.5 versicolor
## 86           6.0         3.4           NA         1.6 versicolor
## 87           6.7         3.1           NA         1.5 versicolor
## 88           6.3         2.3           NA         1.3 versicolor
## 89           5.6         3.0           NA         1.3 versicolor
## 90           5.5         2.5           NA         1.3 versicolor
## 91           5.5         2.6           NA         1.2 versicolor
## 92           6.1         3.0           NA         1.4 versicolor
## 93           5.8         2.6           NA         1.2 versicolor
## 94           5.0         2.3           NA         1.0 versicolor
## 95           5.6         2.7           NA         1.3 versicolor
## 96           5.7         3.0           NA         1.2 versicolor
## 97           5.7         2.9           NA         1.3 versicolor
## 98           6.2         2.9           NA         1.3 versicolor
## 99           5.1         2.5           NA         1.1 versicolor
## 100          5.7         2.8           NA         1.3 versicolor
## 101          6.3         3.3           NA         2.5  virginica
## 102          5.8         2.7           NA         1.9  virginica
## 103          7.1         3.0           NA         2.1  virginica
## 104          6.3         2.9           NA         1.8  virginica
## 105          6.5         3.0           NA         2.2  virginica
## 106          7.6         3.0           NA         2.1  virginica
## 107          4.9         2.5           NA         1.7  virginica
## 108          7.3         2.9           NA         1.8  virginica
## 109          6.7         2.5           NA         1.8  virginica
## 110          7.2         3.6           NA         2.5  virginica
## 111          6.5         3.2           NA         2.0  virginica
## 112          6.4         2.7           NA         1.9  virginica
## 113          6.8         3.0           NA         2.1  virginica
## 114          5.7         2.5           NA         2.0  virginica
## 115          5.8         2.8           NA         2.4  virginica
## 116          6.4         3.2           NA         2.3  virginica
## 117          6.5         3.0           NA         1.8  virginica
## 118          7.7         3.8           NA         2.2  virginica
## 119          7.7         2.6           NA         2.3  virginica
## 120          6.0         2.2           NA         1.5  virginica
## 121          6.9         3.2           NA         2.3  virginica
## 122          5.6         2.8           NA         2.0  virginica
## 123          7.7         2.8           NA         2.0  virginica
## 124          6.3         2.7           NA         1.8  virginica
## 125          6.7         3.3           NA         2.1  virginica
## 126          7.2         3.2           NA         1.8  virginica
## 127          6.2         2.8           NA         1.8  virginica
## 128          6.1         3.0           NA         1.8  virginica
## 129          6.4         2.8           NA         2.1  virginica
## 130          7.2         3.0           NA         1.6  virginica
## 131          7.4         2.8           NA         1.9  virginica
## 132          7.9         3.8           NA         2.0  virginica
## 133          6.4         2.8           NA         2.2  virginica
## 134          6.3         2.8           NA         1.5  virginica
## 135          6.1         2.6           NA         1.4  virginica
## 136          7.7         3.0           NA         2.3  virginica
## 137          6.3         3.4           NA         2.4  virginica
## 138          6.4         3.1           NA         1.8  virginica
## 139          6.0         3.0           NA         1.8  virginica
## 140          6.9         3.1           NA         2.1  virginica
## 141          6.7         3.1           NA         2.4  virginica
## 142          6.9         3.1           NA         2.3  virginica
## 143          5.8         2.7           NA         1.9  virginica
## 144          6.8         3.2           NA         2.3  virginica
## 145          6.7         3.3           NA         2.5  virginica
## 146          6.7         3.0           NA         2.3  virginica
## 147          6.3         2.5           NA         1.9  virginica
## 148          6.5         3.0           NA         2.0  virginica
## 149          6.2         3.4           NA         2.3  virginica
## 150          5.9         3.0           NA         1.8  virginica

Question 2:

Use appropriate map or apply functions, along with scale(), to create a standardized version of the iris dataset. Do this without copy-pasting lines and changing Petal.Length to Petal.Width, etc.

(I recommend looking into map_dfc(), although this is not the only possible solution.)