Benjamin Soltoff
MACS 30500 - Computing for the Social Sciences
University of Chicago
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## lag(): dplyr, statsset.seed(11091987)for loop to square a valueWrite a for loop that calculates the square of each element in a vector.
i in seq_along(x)x, store the new value as the \(i\)th element of the vector outputx <- 1:30
x## [1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
## [24] 24 25 26 27 28 29 30output <- vector("integer", length(x))
for(i in seq_along(x)){
output[[i]] <- x[[i]]^2
}
output## [1] 1 4 9 16 25 36 49 64 81 100 121 144 169 196 225 256 289
## [18] 324 361 400 441 484 529 576 625 676 729 784 841 900map() function to square a valueYou might think to rewrite this function, all we do is:
> map_dbl(x, ^)
Error: unexpected '^' in "map_dbl(x, ^"But that doesn’t work. The exponentiation operator ^ performs a function, but because it isn’t written like a traditional function map_dbl() doesn’t know how to convert this to a for loop. Instead, we need to rewrite it with another function
square <- function(a){
a^2
}
map_dbl(x, square)## [1] 1 4 9 16 25 36 49 64 81 100 121 144 169 196 225 256 289
## [18] 324 361 400 441 484 529 576 625 676 729 784 841 900Here we create a temporary function called square that takes a single argument a. That value is then squared and returned as the output. Now when we write the map function, our data to be mapped over is x and the function to be applied to it is square. We could write this even shorter as:
map_dbl(x, function(a) a^2)## [1] 1 4 9 16 25 36 49 64 81 100 121 144 169 196 225 256 289
## [18] 324 361 400 441 484 529 576 625 676 729 784 841 900This creates a temporary function. It’s temporary because it only exists within the map operation, and therefore it has no name. And since it is so short, we can write on a single line without {}.
devtools::session_info()## Session info --------------------------------------------------------------## setting value
## version R version 3.3.1 (2016-06-21)
## system x86_64, darwin13.4.0
## ui X11
## language (EN)
## collate en_US.UTF-8
## tz America/Chicago
## date 2016-10-13## Packages ------------------------------------------------------------------## package * version date source
## assertthat 0.1 2013-12-06 CRAN (R 3.3.0)
## codetools 0.2-14 2015-07-15 CRAN (R 3.3.1)
## colorspace 1.2-6 2015-03-11 CRAN (R 3.3.0)
## DBI 0.5-1 2016-09-10 CRAN (R 3.3.0)
## devtools 1.12.0 2016-06-24 CRAN (R 3.3.0)
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## dplyr * 0.5.0 2016-06-24 CRAN (R 3.3.0)
## evaluate 0.9 2016-04-29 CRAN (R 3.3.0)
## formatR 1.4 2016-05-09 CRAN (R 3.3.0)
## ggplot2 * 2.1.0.9001 2016-10-01 Github (hadley/ggplot2@feb3ffd)
## gtable 0.2.0 2016-02-26 CRAN (R 3.3.0)
## htmltools 0.3.5 2016-03-21 CRAN (R 3.3.0)
## knitr 1.14 2016-08-13 CRAN (R 3.3.0)
## lazyeval 0.2.0 2016-06-12 CRAN (R 3.3.0)
## magrittr 1.5 2014-11-22 CRAN (R 3.3.0)
## memoise 1.0.0 2016-01-29 CRAN (R 3.3.0)
## munsell 0.4.3 2016-02-13 CRAN (R 3.3.0)
## plyr 1.8.4 2016-06-08 CRAN (R 3.3.0)
## purrr * 0.2.2 2016-06-18 CRAN (R 3.3.0)
## R6 2.1.3 2016-08-19 CRAN (R 3.3.0)
## rcfss 0.1.0 2016-10-06 local
## Rcpp 0.12.7 2016-09-05 cran (@0.12.7)
## readr * 1.0.0 2016-08-03 CRAN (R 3.3.0)
## rmarkdown 1.0.9016 2016-10-08 Github (rstudio/rmarkdown@2158b9d)
## scales 0.4.0 2016-02-26 CRAN (R 3.3.0)
## stringi 1.1.1 2016-05-27 CRAN (R 3.3.0)
## stringr 1.1.0 2016-08-19 cran (@1.1.0)
## tibble * 1.2 2016-08-26 cran (@1.2)
## tidyr * 0.6.0 2016-08-12 CRAN (R 3.3.0)
## tidyverse * 1.0.0 2016-09-09 CRAN (R 3.3.0)
## withr 1.0.2 2016-06-20 CRAN (R 3.3.0)
## yaml 2.1.13 2014-06-12 CRAN (R 3.3.0)