Questions and Answers for Wrangling

Database Used: mtcars.csv

BONUS - Place the original .csv in a github file and have R read from the link. This will be a very useful skill as you progress in your data science education and career.

library(RCurl)
## Loading required package: bitops
x <- getURL("https://raw.githubusercontent.com/jcp9010/R-Week-2-HW-Assignment/master/mtcars.csv")
mtcars.sample <- read.csv(text = x)
  1. Use the summary function to gain an overview of the data set. Then display the mean and median for at least two attributes.
print(mtcars.sample)
##                      X  mpg cyl  disp  hp drat    wt  qsec vs am gear carb
## 1            Mazda RX4 21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
## 2        Mazda RX4 Wag 21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
## 3           Datsun 710 22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
## 4       Hornet 4 Drive 21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
## 5    Hornet Sportabout 18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
## 6              Valiant 18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1
## 7           Duster 360 14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4
## 8            Merc 240D 24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
## 9             Merc 230 22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2
## 10            Merc 280 19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    4
## 11           Merc 280C 17.8   6 167.6 123 3.92 3.440 18.90  1  0    4    4
## 12          Merc 450SE 16.4   8 275.8 180 3.07 4.070 17.40  0  0    3    3
## 13          Merc 450SL 17.3   8 275.8 180 3.07 3.730 17.60  0  0    3    3
## 14         Merc 450SLC 15.2   8 275.8 180 3.07 3.780 18.00  0  0    3    3
## 15  Cadillac Fleetwood 10.4   8 472.0 205 2.93 5.250 17.98  0  0    3    4
## 16 Lincoln Continental 10.4   8 460.0 215 3.00 5.424 17.82  0  0    3    4
## 17   Chrysler Imperial 14.7   8 440.0 230 3.23 5.345 17.42  0  0    3    4
## 18            Fiat 128 32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1
## 19         Honda Civic 30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
## 20      Toyota Corolla 33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1
## 21       Toyota Corona 21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    1
## 22    Dodge Challenger 15.5   8 318.0 150 2.76 3.520 16.87  0  0    3    2
## 23         AMC Javelin 15.2   8 304.0 150 3.15 3.435 17.30  0  0    3    2
## 24          Camaro Z28 13.3   8 350.0 245 3.73 3.840 15.41  0  0    3    4
## 25    Pontiac Firebird 19.2   8 400.0 175 3.08 3.845 17.05  0  0    3    2
## 26           Fiat X1-9 27.3   4  79.0  66 4.08 1.935 18.90  1  1    4    1
## 27       Porsche 914-2 26.0   4 120.3  91 4.43 2.140 16.70  0  1    5    2
## 28        Lotus Europa 30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2
## 29      Ford Pantera L 15.8   8 351.0 264 4.22 3.170 14.50  0  1    5    4
## 30        Ferrari Dino 19.7   6 145.0 175 3.62 2.770 15.50  0  1    5    6
## 31       Maserati Bora 15.0   8 301.0 335 3.54 3.570 14.60  0  1    5    8
## 32          Volvo 142E 21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2
print(summary(mtcars.sample))
##                   X           mpg             cyl             disp      
##  AMC Javelin       : 1   Min.   :10.40   Min.   :4.000   Min.   : 71.1  
##  Cadillac Fleetwood: 1   1st Qu.:15.43   1st Qu.:4.000   1st Qu.:120.8  
##  Camaro Z28        : 1   Median :19.20   Median :6.000   Median :196.3  
##  Chrysler Imperial : 1   Mean   :20.09   Mean   :6.188   Mean   :230.7  
##  Datsun 710        : 1   3rd Qu.:22.80   3rd Qu.:8.000   3rd Qu.:326.0  
##  Dodge Challenger  : 1   Max.   :33.90   Max.   :8.000   Max.   :472.0  
##  (Other)           :26                                                  
##        hp             drat             wt             qsec      
##  Min.   : 52.0   Min.   :2.760   Min.   :1.513   Min.   :14.50  
##  1st Qu.: 96.5   1st Qu.:3.080   1st Qu.:2.581   1st Qu.:16.89  
##  Median :123.0   Median :3.695   Median :3.325   Median :17.71  
##  Mean   :146.7   Mean   :3.597   Mean   :3.217   Mean   :17.85  
##  3rd Qu.:180.0   3rd Qu.:3.920   3rd Qu.:3.610   3rd Qu.:18.90  
##  Max.   :335.0   Max.   :4.930   Max.   :5.424   Max.   :22.90  
##                                                                 
##        vs               am              gear            carb      
##  Min.   :0.0000   Min.   :0.0000   Min.   :3.000   Min.   :1.000  
##  1st Qu.:0.0000   1st Qu.:0.0000   1st Qu.:3.000   1st Qu.:2.000  
##  Median :0.0000   Median :0.0000   Median :4.000   Median :2.000  
##  Mean   :0.4375   Mean   :0.4062   Mean   :3.688   Mean   :2.812  
##  3rd Qu.:1.0000   3rd Qu.:1.0000   3rd Qu.:4.000   3rd Qu.:4.000  
##  Max.   :1.0000   Max.   :1.0000   Max.   :5.000   Max.   :8.000  
## 
# Mean and Median for MPG of all cars within database mtcars.sample
print(paste0("The mean MPG of all cars within database mtcars.sample is: ", mean(mtcars.sample$mpg)))
## [1] "The mean MPG of all cars within database mtcars.sample is: 20.090625"
print(paste0("The median MPG of all cars within database mtcars.sample is: ", median(mtcars.sample$mpg)))
## [1] "The median MPG of all cars within database mtcars.sample is: 19.2"
print(paste0("The mean HP of all cars within database mtcars.sample is: ", mean(mtcars.sample$hp)))
## [1] "The mean HP of all cars within database mtcars.sample is: 146.6875"
print(paste0("The median HP of all cars within database mtcars.sample is: ", median(mtcars.sample$hp)))
## [1] "The median HP of all cars within database mtcars.sample is: 123"
  1. Create a new data frame with a subset of the columns and rows. Make sure to rename it.
# New data frame set called df.mtcars, which contains a subset of cars that have MPG > 20
df.mtcars <- subset(mtcars.sample, mpg > 20)
print(df.mtcars)
##                 X  mpg cyl  disp  hp drat    wt  qsec vs am gear carb
## 1       Mazda RX4 21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
## 2   Mazda RX4 Wag 21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
## 3      Datsun 710 22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
## 4  Hornet 4 Drive 21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
## 8       Merc 240D 24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
## 9        Merc 230 22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2
## 18       Fiat 128 32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1
## 19    Honda Civic 30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
## 20 Toyota Corolla 33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1
## 21  Toyota Corona 21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    1
## 26      Fiat X1-9 27.3   4  79.0  66 4.08 1.935 18.90  1  1    4    1
## 27  Porsche 914-2 26.0   4 120.3  91 4.43 2.140 16.70  0  1    5    2
## 28   Lotus Europa 30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2
## 32     Volvo 142E 21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2

If I were to create a brand new data.frame altogether, an example is shown below:

x <- 1:10
y <- letters[1:10]
z <- c(T,F,T,T,F,F,F,T,T,T)
a <- sample(1:100, 10)
b <- sample(1:1000, 10)

df <- data.frame(x,y,z,a, b)
print(df)
##     x y     z  a   b
## 1   1 a  TRUE 81 242
## 2   2 b FALSE 35 500
## 3   3 c  TRUE 62 446
## 4   4 d  TRUE  3 175
## 5   5 e FALSE  5 818
## 6   6 f FALSE 26 393
## 7   7 g FALSE 78 284
## 8   8 h  TRUE 46 678
## 9   9 i  TRUE  1 841
## 10 10 j  TRUE 22 101
colnames(df) <- c("Numbers","Letters","Boolean","Random1","Random2")
print(df)
##    Numbers Letters Boolean Random1 Random2
## 1        1       a    TRUE      81     242
## 2        2       b   FALSE      35     500
## 3        3       c    TRUE      62     446
## 4        4       d    TRUE       3     175
## 5        5       e   FALSE       5     818
## 6        6       f   FALSE      26     393
## 7        7       g   FALSE      78     284
## 8        8       h    TRUE      46     678
## 9        9       i    TRUE       1     841
## 10      10       j    TRUE      22     101
  1. Create new column names for the new data frame. (Now going back to df.mtcars)
df.mtcars$Power.To.Weight <- (df.mtcars$hp/df.mtcars$wt)
df.mtcars$Distance.Traveled.On.Ten.Gallons <- (df.mtcars$mpg * 10)

print(df.mtcars)
##                 X  mpg cyl  disp  hp drat    wt  qsec vs am gear carb
## 1       Mazda RX4 21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
## 2   Mazda RX4 Wag 21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
## 3      Datsun 710 22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
## 4  Hornet 4 Drive 21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
## 8       Merc 240D 24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
## 9        Merc 230 22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2
## 18       Fiat 128 32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1
## 19    Honda Civic 30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
## 20 Toyota Corolla 33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1
## 21  Toyota Corona 21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    1
## 26      Fiat X1-9 27.3   4  79.0  66 4.08 1.935 18.90  1  1    4    1
## 27  Porsche 914-2 26.0   4 120.3  91 4.43 2.140 16.70  0  1    5    2
## 28   Lotus Europa 30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2
## 32     Volvo 142E 21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2
##    Power.To.Weight Distance.Traveled.On.Ten.Gallons
## 1         41.98473                              210
## 2         38.26087                              210
## 3         40.08621                              228
## 4         34.21462                              214
## 8         19.43574                              244
## 9         30.15873                              228
## 18        30.00000                              324
## 19        32.19814                              304
## 20        35.42234                              339
## 21        39.35091                              215
## 26        34.10853                              273
## 27        42.52336                              260
## 28        74.68605                              304
## 32        39.20863                              214
  1. Use the summary function to create an overview of your new data frame. Print the mean and median for the same two attributes. Please compare.
print(summary(df.mtcars))
##               X          mpg             cyl             disp       
##  Datsun 710    :1   Min.   :21.00   Min.   :4.000   Min.   : 71.10  
##  Fiat 128      :1   1st Qu.:21.43   1st Qu.:4.000   1st Qu.: 83.03  
##  Fiat X1-9     :1   Median :23.60   Median :4.000   Median :120.20  
##  Honda Civic   :1   Mean   :25.48   Mean   :4.429   Mean   :123.89  
##  Hornet 4 Drive:1   3rd Qu.:29.62   3rd Qu.:4.000   3rd Qu.:145.22  
##  Lotus Europa  :1   Max.   :33.90   Max.   :6.000   Max.   :258.00  
##  (Other)       :8                                                   
##        hp             drat             wt             qsec      
##  Min.   : 52.0   Min.   :3.080   Min.   :1.513   Min.   :16.46  
##  1st Qu.: 66.0   1st Qu.:3.790   1st Qu.:1.986   1st Qu.:17.39  
##  Median : 94.0   Median :3.910   Median :2.393   Median :18.75  
##  Mean   : 88.5   Mean   :3.976   Mean   :2.418   Mean   :18.82  
##  3rd Qu.:109.8   3rd Qu.:4.103   3rd Qu.:2.851   3rd Qu.:19.79  
##  Max.   :113.0   Max.   :4.930   Max.   :3.215   Max.   :22.90  
##                                                                 
##        vs               am              gear        carb      
##  Min.   :0.0000   Min.   :0.0000   Min.   :3   Min.   :1.000  
##  1st Qu.:1.0000   1st Qu.:0.2500   1st Qu.:4   1st Qu.:1.000  
##  Median :1.0000   Median :1.0000   Median :4   Median :2.000  
##  Mean   :0.7857   Mean   :0.7143   Mean   :4   Mean   :1.857  
##  3rd Qu.:1.0000   3rd Qu.:1.0000   3rd Qu.:4   3rd Qu.:2.000  
##  Max.   :1.0000   Max.   :1.0000   Max.   :5   Max.   :4.000  
##                                                               
##  Power.To.Weight Distance.Traveled.On.Ten.Gallons
##  Min.   :19.44   Min.   :210.0                   
##  1st Qu.:32.68   1st Qu.:214.2                   
##  Median :36.84   Median :236.0                   
##  Mean   :37.97   Mean   :254.8                   
##  3rd Qu.:39.90   3rd Qu.:296.2                   
##  Max.   :74.69   Max.   :339.0                   
## 
print(paste0("The mean MPG of all cars within database mtcars.sample is: ", mean(mtcars.sample$mpg)))
## [1] "The mean MPG of all cars within database mtcars.sample is: 20.090625"
print(paste0("The mean MPG of all cars within database df.mtcars is: ", mean(df.mtcars$mpg)))
## [1] "The mean MPG of all cars within database df.mtcars is: 25.4785714285714"
print(paste0("The median MPG of all cars within database mtcars.sample is: ", median(mtcars.sample$mpg)))
## [1] "The median MPG of all cars within database mtcars.sample is: 19.2"
print(paste0("The median MPG of all cars within database df.mtcars is: ", median(df.mtcars$mpg)))
## [1] "The median MPG of all cars within database df.mtcars is: 23.6"
print(paste0("The mean HP of all cars within database mtcars.sample is: ", mean(mtcars.sample$hp)))
## [1] "The mean HP of all cars within database mtcars.sample is: 146.6875"
print(paste0("The mean HP of all cars within database df.mtcars is: ", mean(df.mtcars$hp)))
## [1] "The mean HP of all cars within database df.mtcars is: 88.5"
print(paste0("The median HP of all cars within database mtcars.sample is: ", median(mtcars.sample$hp)))
## [1] "The median HP of all cars within database mtcars.sample is: 123"
print(paste0("The median HP of all cars within database df.mtcars is: ", median(df.mtcars$hp)))
## [1] "The median HP of all cars within database df.mtcars is: 94"
  1. For at least 3 values in a column, please rename so that every value in that column is renamed. For example, suppose I have 20 values of the letter “e” in one column. Rename those values so that all 20 would show as “excellent.”
i <- 1
for (row in df.mtcars$cyl){
  if (row == 6){
    df.mtcars[[i,'cyl']] <- "Six Cylinders"
  }else if (row == 8){
    df.mtcars[[i,'cyl']] <- "Eight Cylinders"
  }else if (row == 4){
    df.mtcars[[i,'cyl']] <- "Four Cylinders"
  }
  i <- i + 1
}

print(df.mtcars)
##                 X  mpg            cyl  disp  hp drat    wt  qsec vs am
## 1       Mazda RX4 21.0  Six Cylinders 160.0 110 3.90 2.620 16.46  0  1
## 2   Mazda RX4 Wag 21.0  Six Cylinders 160.0 110 3.90 2.875 17.02  0  1
## 3      Datsun 710 22.8 Four Cylinders 108.0  93 3.85 2.320 18.61  1  1
## 4  Hornet 4 Drive 21.4  Six Cylinders 258.0 110 3.08 3.215 19.44  1  0
## 8       Merc 240D 24.4 Four Cylinders 146.7  62 3.69 3.190 20.00  1  0
## 9        Merc 230 22.8 Four Cylinders 140.8  95 3.92 3.150 22.90  1  0
## 18       Fiat 128 32.4 Four Cylinders  78.7  66 4.08 2.200 19.47  1  1
## 19    Honda Civic 30.4 Four Cylinders  75.7  52 4.93 1.615 18.52  1  1
## 20 Toyota Corolla 33.9 Four Cylinders  71.1  65 4.22 1.835 19.90  1  1
## 21  Toyota Corona 21.5 Four Cylinders 120.1  97 3.70 2.465 20.01  1  0
## 26      Fiat X1-9 27.3 Four Cylinders  79.0  66 4.08 1.935 18.90  1  1
## 27  Porsche 914-2 26.0 Four Cylinders 120.3  91 4.43 2.140 16.70  0  1
## 28   Lotus Europa 30.4 Four Cylinders  95.1 113 3.77 1.513 16.90  1  1
## 32     Volvo 142E 21.4 Four Cylinders 121.0 109 4.11 2.780 18.60  1  1
##    gear carb Power.To.Weight Distance.Traveled.On.Ten.Gallons
## 1     4    4        41.98473                              210
## 2     4    4        38.26087                              210
## 3     4    1        40.08621                              228
## 4     3    1        34.21462                              214
## 8     4    2        19.43574                              244
## 9     4    2        30.15873                              228
## 18    4    1        30.00000                              324
## 19    4    2        32.19814                              304
## 20    4    1        35.42234                              339
## 21    3    1        39.35091                              215
## 26    4    1        34.10853                              273
## 27    5    2        42.52336                              260
## 28    5    2        74.68605                              304
## 32    4    2        39.20863                              214

Also to demonstrate that the eight cylinders will take place for 8, I will run this code for mtcars.sample

i <- 1
for (row in mtcars.sample$cyl){
  if (row == 6){
    mtcars.sample[[i,'cyl']] <- "Six Cylinders"
  }else if (row == 8){
    mtcars.sample[[i,'cyl']] <- "Eight Cylinders"
  }else if (row == 4){
    mtcars.sample[[i,'cyl']] <- "Four Cylinders"
  }
  i <- i + 1
}

print(mtcars.sample)
##                      X  mpg             cyl  disp  hp drat    wt  qsec vs
## 1            Mazda RX4 21.0   Six Cylinders 160.0 110 3.90 2.620 16.46  0
## 2        Mazda RX4 Wag 21.0   Six Cylinders 160.0 110 3.90 2.875 17.02  0
## 3           Datsun 710 22.8  Four Cylinders 108.0  93 3.85 2.320 18.61  1
## 4       Hornet 4 Drive 21.4   Six Cylinders 258.0 110 3.08 3.215 19.44  1
## 5    Hornet Sportabout 18.7 Eight Cylinders 360.0 175 3.15 3.440 17.02  0
## 6              Valiant 18.1   Six Cylinders 225.0 105 2.76 3.460 20.22  1
## 7           Duster 360 14.3 Eight Cylinders 360.0 245 3.21 3.570 15.84  0
## 8            Merc 240D 24.4  Four Cylinders 146.7  62 3.69 3.190 20.00  1
## 9             Merc 230 22.8  Four Cylinders 140.8  95 3.92 3.150 22.90  1
## 10            Merc 280 19.2   Six Cylinders 167.6 123 3.92 3.440 18.30  1
## 11           Merc 280C 17.8   Six Cylinders 167.6 123 3.92 3.440 18.90  1
## 12          Merc 450SE 16.4 Eight Cylinders 275.8 180 3.07 4.070 17.40  0
## 13          Merc 450SL 17.3 Eight Cylinders 275.8 180 3.07 3.730 17.60  0
## 14         Merc 450SLC 15.2 Eight Cylinders 275.8 180 3.07 3.780 18.00  0
## 15  Cadillac Fleetwood 10.4 Eight Cylinders 472.0 205 2.93 5.250 17.98  0
## 16 Lincoln Continental 10.4 Eight Cylinders 460.0 215 3.00 5.424 17.82  0
## 17   Chrysler Imperial 14.7 Eight Cylinders 440.0 230 3.23 5.345 17.42  0
## 18            Fiat 128 32.4  Four Cylinders  78.7  66 4.08 2.200 19.47  1
## 19         Honda Civic 30.4  Four Cylinders  75.7  52 4.93 1.615 18.52  1
## 20      Toyota Corolla 33.9  Four Cylinders  71.1  65 4.22 1.835 19.90  1
## 21       Toyota Corona 21.5  Four Cylinders 120.1  97 3.70 2.465 20.01  1
## 22    Dodge Challenger 15.5 Eight Cylinders 318.0 150 2.76 3.520 16.87  0
## 23         AMC Javelin 15.2 Eight Cylinders 304.0 150 3.15 3.435 17.30  0
## 24          Camaro Z28 13.3 Eight Cylinders 350.0 245 3.73 3.840 15.41  0
## 25    Pontiac Firebird 19.2 Eight Cylinders 400.0 175 3.08 3.845 17.05  0
## 26           Fiat X1-9 27.3  Four Cylinders  79.0  66 4.08 1.935 18.90  1
## 27       Porsche 914-2 26.0  Four Cylinders 120.3  91 4.43 2.140 16.70  0
## 28        Lotus Europa 30.4  Four Cylinders  95.1 113 3.77 1.513 16.90  1
## 29      Ford Pantera L 15.8 Eight Cylinders 351.0 264 4.22 3.170 14.50  0
## 30        Ferrari Dino 19.7   Six Cylinders 145.0 175 3.62 2.770 15.50  0
## 31       Maserati Bora 15.0 Eight Cylinders 301.0 335 3.54 3.570 14.60  0
## 32          Volvo 142E 21.4  Four Cylinders 121.0 109 4.11 2.780 18.60  1
##    am gear carb
## 1   1    4    4
## 2   1    4    4
## 3   1    4    1
## 4   0    3    1
## 5   0    3    2
## 6   0    3    1
## 7   0    3    4
## 8   0    4    2
## 9   0    4    2
## 10  0    4    4
## 11  0    4    4
## 12  0    3    3
## 13  0    3    3
## 14  0    3    3
## 15  0    3    4
## 16  0    3    4
## 17  0    3    4
## 18  1    4    1
## 19  1    4    2
## 20  1    4    1
## 21  0    3    1
## 22  0    3    2
## 23  0    3    2
## 24  0    3    4
## 25  0    3    2
## 26  1    4    1
## 27  1    5    2
## 28  1    5    2
## 29  1    5    4
## 30  1    5    6
## 31  1    5    8
## 32  1    4    2
  1. Display enough rows to see examples of all of steps 1 - 5 above.