Example 5-73 Selecting Rows by Position

MTCARS <- ore.push(mtcars)
# Display the names of the rows in MTCARS
rownames(MTCARS)
# Select the first row
slice(MTCARS, 1L)

# Arrange the rows by horsepower, then select the first row by position
MTCARS <- arrange(MTCARS, hp)
slice(MTCARS, 1L)

by_cyl <- group_by(MTCARS, cyl)
# Grouping is ignored by slice.
slice(by_cyl, 1:2)
# Use filter and row_number to obtain slices per group.
filter(by_cyl, row_number(hp) < 3L) 

Listing for This Example

R> MTCARS <- ore.push(mtcars)
R> # Display the names of the rows in MTCARS
R> rownames(MTCARS)
 [1] "Mazda RX4"           "Mazda RX4 Wag"       "Datsun 710"          "Hornet 4 Drive"      "Hornet Sportabout"  
 [6] "Valiant"             "Duster 360"          "Merc 240D"           "Merc 230"            "Merc 280"           
[11] "Merc 280C"           "Merc 450SE"          "Merc 450SL"          "Merc 450SLC"         "Cadillac Fleetwood" 
[16] "Lincoln Continental" "Chrysler Imperial"   "Fiat 128"            "Honda Civic"         "Toyota Corolla"     
[21] "Toyota Corona"       "Dodge Challenger"    "AMC Javelin"         "Camaro Z28"          "Pontiac Firebird"   
[26] "Fiat X1-9"           "Porsche 914-2"       "Lotus Europa"        "Ford Pantera L"      "Ferrari Dino"       
[31] "Maserati Bora"       "Volvo 142E"  
R> # Select the first row
R> slice(MTCARS, 1L)
          mpg cyl disp  hp drat   wt  qsec vs am gear carb
Mazda RX4  21   6  160 110  3.9 2.62 16.46  0  1    4    4
R>
R> # Arrange the rows by horsepower, then select the first row by position
R> MTCARS <- arrange(MTCARS, hp)
R> slice(MTCARS, 1L)
   mpg cyl disp hp drat    wt  qsec vs am gear carb
1 30.4   4 75.7 52 4.93 1.615 18.52  1  1    4    2
R>
R> by_cyl <- group_by(MTCARS, cyl)
R> # Grouping is ignored by slice
R> slice(by_cyl, 1:2)
   mpg cyl  disp hp drat    wt  qsec vs am gear carb
1 30.4   4  75.7 52 4.93 1.615 18.52  1  1    4    2
2 24.4   4 146.7 62 3.69 3.190 20.00  1  0    4    2
Warning message:
In slice_.ore.frame(.data, .dots = .ore.dplyr.exprall(..., env = parent.frame())) :
  grouping is ignored
R> # Use filter and row_number to obtain slices per group
R> filter(by_cyl, row_number(hp) < 3L)
   mpg cyl  disp  hp drat    wt  qsec vs am gear carb
1 30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
2 24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
3 18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1
4 21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
5 15.2   8 304.0 150 3.15 3.435 17.30  0  0    3    2
6 15.5   8 318.0 150 2.76 3.520 16.87  0  0    3    2