What does the tilde mean in this context of R code [duplicate]

Question

1. Fx=purrr::map(CDF, ~ tibble(
                       severity=severities$severity,
                       inclusive=severities$inclusive,
                       Fx=.x(severities$severity, severities$inclusive))))
   

2. raw_df <- tibble::tribble(
       ~"segment", ~"limit", ~"attach", ~"pct_written", ~"premium", ~"product", ~"lalae_ratio",
       "",    50000,      1000,            0.5,     273456,    "prod1",           0.65,
       "",    20000,      2000,            0.5,     285760,    "prod2",           0.65,
       "",    2e+05,      3000,            0.5,     956456,    "prod3",           0.65,
       "",    10000,       300,            0.5,      90890,    "prod4",           0.65)
   

I can sort of guess it, but I do not have a precise definition of what it does.

This is different from:

dependent_variable ~ independent_variables

Answer 1

The tilde operator in R is a general operator that creates a formula object.

However, the usage in your specific pieces of code is a special case of that: purrr co-opts formulas to implement an anonymous function notation. You can read more in the purrr introduction. But briefly, the usage

purrr::map(data, ~ expression_with(.x))

Is equivalent to

purrr::map(data, function (.x) expression_with(.x))

The second piece of code does something different still, and that usage is described in the documentation of the tribble function.