Last updated: 2019-09-27

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Setup

library(tidyverse)

Exercises

p. 123

How can you tell if an object is a tibble? (Hint: try printing mtcars, which is a regular data frame).

class(mtcars)
[1] "data.frame"
class(as_tibble(mtcars))
[1] "tbl_df"     "tbl"        "data.frame"

Compare and contrast the following operations on a data.frame and equivalent tibble. What is different? Why might the default data frame behaviours cause you frustration?

# data frame
df <- data.frame(abc = 1, xyz = "a")
df$x # Gives you a result (column xyz) even though column x does not exist
[1] a
Levels: a
df[, "xyz"] # returns a vector, string coerced to factor
[1] a
Levels: a
df[, c("abc", "xyz")] # returns a data frame
  abc xyz
1   1   a
# tibble
dft <- tibble(abc = 1, xyz = "a")
dft$x # warns that column x does not exist
Warning: Unknown or uninitialised column: 'x'.
NULL
dft[, "xyz"] # returns tibble, string remains string
# A tibble: 1 x 1
  xyz  
  <chr>
1 a    
dft[, c("abc", "xyz")] # returns tibble
# A tibble: 1 x 2
    abc xyz  
  <dbl> <chr>
1     1 a

If you have the name of a variable stored in an object, e.g. var <- "mpg", how can you extract the reference variable from a tibble?

var <- "mpg"
head(mtcars[, var])
[1] 21.0 21.0 22.8 21.4 18.7 18.1
head(as_tibble(mtcars)[, var])
# A tibble: 6 x 1
    mpg
  <dbl>
1  21  
2  21  
3  22.8
4  21.4
5  18.7
6  18.1

Practice referring to non-syntactic names in the following data frame by: Extracting the variable called 1. Plotting a scatterplot of 1 vs 2. Creating a new column called 3 which is 2 divided by 1.

Renaming the columns to one, two and three.

annoying <- tibble(
  `1` = 1:10,
  `2` = `1` * 2 + rnorm(length(`1`))
)
annoying$`1`
 [1]  1  2  3  4  5  6  7  8  9 10
annoying[["1"]]
 [1]  1  2  3  4  5  6  7  8  9 10
ggplot(annoying, aes(`1`, `2`)) + geom_point()

annoying <- annoying %>%
  mutate(`3` = `1` + `2`)
annoying %>% rename(one = `1`, two = `2`, three = `3`)
# A tibble: 10 x 3
     one   two three
   <int> <dbl> <dbl>
 1     1  2.20  3.20
 2     2  3.16  5.16
 3     3  5.71  8.71
 4     4  6.51 10.5 
 5     5  8.80 13.8 
 6     6 11.6  17.6 
 7     7 14.8  21.8 
 8     8 15.9  23.9 
 9     9 17.7  26.7 
10    10 19.9  29.9

What does tibble::enframe() do? When might you use it?

Converts a named vector/list to a 2-column data frame.

What option controls how many additional column names are printed at the footer of a tibble?

tibble.max_extra_cols: Number of extra columns printed in reduced form. Default: 100.


sessionInfo()
R version 3.6.1 (2019-07-05)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 18.04.3 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/atlas/libblas.so.3.10.3
LAPACK: /usr/lib/x86_64-linux-gnu/atlas/liblapack.so.3.10.3

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] forcats_0.4.0   stringr_1.4.0   dplyr_0.8.3     purrr_0.3.2    
[5] readr_1.3.1     tidyr_1.0.0     tibble_2.1.3    ggplot2_3.2.1  
[9] tidyverse_1.2.1

loaded via a namespace (and not attached):
 [1] tidyselect_0.2.5  xfun_0.9          haven_2.1.1      
 [4] lattice_0.20-38   colorspace_1.4-1  vctrs_0.2.0      
 [7] generics_0.0.2    htmltools_0.3.6   yaml_2.2.0       
[10] utf8_1.1.4        rlang_0.4.0       pillar_1.4.2     
[13] glue_1.3.1        withr_2.1.2       modelr_0.1.5     
[16] readxl_1.3.1      lifecycle_0.1.0   munsell_0.5.0    
[19] gtable_0.3.0      workflowr_1.4.0   cellranger_1.1.0 
[22] rvest_0.3.4       evaluate_0.14     labeling_0.3     
[25] knitr_1.25        fansi_0.4.0       broom_0.5.2      
[28] Rcpp_1.0.2        scales_1.0.0      backports_1.1.4  
[31] jsonlite_1.6      fs_1.3.1          hms_0.5.1        
[34] digest_0.6.21     stringi_1.4.3     grid_3.6.1       
[37] rprojroot_1.2     cli_1.1.0         tools_3.6.1      
[40] magrittr_1.5      lazyeval_0.2.2    crayon_1.3.4     
[43] pkgconfig_2.0.2   zeallot_0.1.0     xml2_1.2.2       
[46] lubridate_1.7.4   assertthat_0.2.1  rmarkdown_1.15   
[49] httr_1.4.1        rstudioapi_0.10   R6_2.4.0         
[52] nlme_3.1-141      git2r_0.26.1.9000 compiler_3.6.1