2025-03-05

Data Frames

1. Make a data frame with 3 columns and 5 rows in which:

• The first column contains the sequence of numbers from 1 to 5
• The second column contains a character vector
• The third column contains a logical vector

df=cbind.data.frame(N=1:5, A=c("a", "b", "c", "d", "e"),C=c(TRUE, FALSE, TRUE, FALSE, TRUE) )

df

##   N A     C
## 1 1 a  TRUE
## 2 2 b FALSE
## 3 3 c  TRUE
## 4 4 d FALSE
## 5 5 e  TRUE

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2. Extract the first two columns and first two rows. HINT: Use the same notation as matrices.

df[1:2, 1:2]

##   N A
## 1 1 a
## 2 2 b

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3. Extract the second column using the column names. You can use [ ] or $; use both the method in two different answers.

df[,"A"]

## [1] "a" "b" "c" "d" "e"

df$A

## [1] "a" "b" "c" "d" "e"

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4. Extract rows where the 1st column is larger than 3. HINT: You can get a logical vector using the > operator, and logical vectors can be used in [ ] when subsetting.

df[df$N>3,]

##   N A     C
## 4 4 d FALSE
## 5 5 e  TRUE

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5. Convert the data frame to the matrix format. HINT: Use as.matrix(). Observe what happens to numeric and logical values in the data frame.

as.matrix(df)

##      N   A   C      
## [1,] "1" "a" "TRUE" 
## [2,] "2" "b" "FALSE"
## [3,] "3" "c" "TRUE" 
## [4,] "4" "d" "FALSE"
## [5,] "5" "e" "TRUE"

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Lists

6. Make a list using the list() function. Your list should have 4 elements:

• two vectors (a logical one and a numeric one)
• a matrix
• a data frame.

el1=1:100
el2=c(rep(FALSE, 10), rep(TRUE, 20))

m=matrix(1:25, byrow = T, ncol=5)

l=cbind.data.frame(name=c("Gio", "Rob", "Anne"), age=c(12, 15, 17))

lista=list(el1, el2, m, l)

lista

## [[1]]
##   [1]   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15  16  17  18
##  [19]  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36
##  [37]  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54
##  [55]  55  56  57  58  59  60  61  62  63  64  65  66  67  68  69  70  71  72
##  [73]  73  74  75  76  77  78  79  80  81  82  83  84  85  86  87  88  89  90
##  [91]  91  92  93  94  95  96  97  98  99 100
## 
## [[2]]
##  [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE
## [13]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
## [25]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
## 
## [[3]]
##      [,1] [,2] [,3] [,4] [,5]
## [1,]    1    2    3    4    5
## [2,]    6    7    8    9   10
## [3,]   11   12   13   14   15
## [4,]   16   17   18   19   20
## [5,]   21   22   23   24   25
## 
## [[4]]
##   name age
## 1  Gio  12
## 2  Rob  15
## 3 Anne  17

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7. Extract the first column of the matrix contained in the list.

lista[[3]][,1]

## [1]  1  6 11 16 21

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