across function not found in dplyr package [duplicate]

Question

I want to use the across() function in dplyr but get an error. For instance, running

iris %>%
  group_by(Species) %>%
  summarise(across(starts_with("Sepal"), mean))

gives me

Error in across(starts_with("Sepal"), mean) : 
  could not find function "across"

across() is a recent introduction https://towardsdatascience.com/what-you-need-to-know-about-the-new-dplyr-1-0-0-7eaaaf6d78ac in dplyr. However, the package dplyr is updated and loaded

packageVersion('dplyr')
[1] ‘1.0.0’

Checking inside dplyr

ls("package:dplyr")
  [1] "%>%"                   "add_count"             "add_count_"            "add_row"               "add_rownames"          "add_tally"            
  [7] "add_tally_"            "all_equal"             "all_vars"              "anti_join"             "any_vars"              "arrange"              
 [13] "arrange_"              "arrange_all"           "arrange_at"            "arrange_if"            "as_data_frame"         "as_label" 

I find that across does not exist, however if I look the function up in the helper ?across I get the classic page explaining the functionalities of across.

How to get across to work?

----- EDIT -----

My sessionInfo() is as follows:

> sessionInfo()
R version 3.6.1 (2019-07-05)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS Mojave 10.14.6

Matrix products: default
BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

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

other attached packages:
[1] tidyselect_1.1.0 dplyr_1.0.0     

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.3       cellranger_1.1.0 pillar_1.4.2     compiler_3.6.1   forcats_0.4.0    tools_3.6.1      jsonlite_1.6     lubridate_1.7.4  lifecycle_0.2.0 
[10] tibble_2.1.3     nlme_3.1-140     gtable_0.3.0     lattice_0.20-38  pkgconfig_2.0.3  rlang_0.4.6      cli_1.1.0        rstudioapi_0.10  haven_2.1.1     
[19] xml2_1.2.2       httr_1.4.1       stringr_1.4.0    generics_0.0.2   vctrs_0.3.1      hms_0.5.1        grid_3.6.1       glue_1.4.1       R6_2.4.0        
[28] fansi_0.4.0      readxl_1.3.1     readr_1.3.1      modelr_0.1.5     tidyr_1.0.0      purrr_0.3.3      ggplot2_3.2.1    magrittr_1.5     backports_1.1.4 
[37] scales_1.0.0     rvest_0.3.4      assertthat_0.2.1 tidyverse_1.2.1  colorspace_1.4-1 utf8_1.1.4       stringi_1.4.3    lazyeval_0.2.2   munsell_0.5.0   
[46] broom_0.5.2      crayon_1.3.4    
> .libPaths()
[1] "/Library/Frameworks/R.framework/Versions/3.6/Resources/library"

Answer 1

The across function is available only in the development version of dplyr, not on CRAN yet to use the accross function install dplyr dev version by using the code below

install.packages("devtools")

library(devtools)
devtools::install_github("tidyverse/dplyr")
library(dplyr)

now your code should work

data("iris")
iris %>%
  group_by(Species) %>%
  summarise(across(starts_with("Sepal"), mean))

output

# A tibble: 3 x 3
  Species    Sepal.Length Sepal.Width
  <fct>             <dbl>       <dbl>
1 setosa             5.01        3.43
2 versicolor         5.94        2.77
3 virginica          6.59        2.97