What is meaning of first tilde in purrr::map

by

As per the map help documentation, map needs a function but it also accepts a formula, character vector, numeric vector, or list, the latter of which are converted to functions.

The ~ operator in R creates formula. So ~ lm(mpg ~ wt, data = .) is a formula. Formulas are useful in R because they prevent immediate evaluation of symbols. For example you can define

x <- ~f(a+b)

without f, a or b being defined anywhere. In this case ~ lm(mpg ~ wt, data = .) is basically a shortcut for function(x) {lm(mpg ~ wt, data = x)} because map can change the value of . in the formula as needed.

Without the tilde, lm(mpg ~ wt, data = .) is just an expression or call in R that’s evaluated immediately. The . wouldn’t be defined at the time that’s called and map can’t convert that into a function.

You can turn these formulas into functions outside of the map() with purrr::as_mapper() function. For example

myfun <- as_mapper(~lm(mpg ~ wt, data = .))
myfun(mtcars)
# Call:
# lm(formula = mpg ~ wt, data = .)
# 
# Coefficients:
# (Intercept)           wt  
#      37.285       -5.344  

myfun
# <lambda>
# function (..., .x = ..1, .y = ..2, . = ..1) 
# lm(mpg ~ wt, data = .)
# attr(,"class")
# [1] "rlang_lambda_function"

You can see how the . becomes the first parameter that’s passed to that function.

More Related Contents:

  1. Why use purrr::map instead of lapply?
  2. In R formulas, why do I have to use the I() function on power terms, like y ~ I(x^3)
  3. How to use map from purrr with dplyr::mutate to create multiple new columns based on column pairs
  4. purrr map equivalent of nested for loop
  5. tidyverse – prefered way to turn a named vector into a data.frame/tibble
  6. Harnessing .f list names with purrr::pmap
  7. loess regression on each group with dplyr::group_by()
  8. Adding column if it does not exist
  9. Show correlations as an ordered list, not as a large matrix
  10. set date range in ggplot
  11. Linear model function lm() error: NA/NaN/Inf in foreign function call (arg 1)
  12. Should I avoid programming packages with pipe operators?
  13. data.table package in R 3.5 does not install
  14. horizontal dendrogram in R with labels
  15. Reading big data with fixed width
  16. Got message unable to load shared object stats.so when R starts
  17. Read FASTA into a dataframe and extract subsequences of FASTA file
  18. cbind: is there a way to have missing values set to NA?
  19. Get selected rows of Rhandsontable
  20. How to add Latex code in ggplot2 legend labels?
  21. Dictionary() is not supported anymore in tm package. How to emend code?
  22. How to divide a number of columns by one column?
  23. Download All Files From a Folder on a Website
  24. R install package loaded namespace
  25. 3d plot in R – Patch
  26. Sparse matrix to a data frame in R
  27. Error in loading rgl package with Mac OS X
  28. Why does as_tibble() round floats to the nearest integer?
  29. RStudio Shiny list from checking rows in dataTables
  30. Too many labels on axis

Leave a Comment