Installing data.table R package on M1 Macs

 For data.table install, if you plan on using multiple threads, you have to enable it during installation/compilation. When loading the package, you will see a warning that says

data.table 1.x.x using 1 threads (see ?getDTthreads). 

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This installation of data.table has not detected OpenMP support. It should still work but in single-threaded mode. This is a Mac.

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Just go to this link:

https://github.com/Rdatatable/data.table/wiki/Installation

0. May need to install gfortran 

brew install gfortran

and these lines are needed in ~/.R/makevars file:

LDFLAGS += -L/opt/homebrew/opt/libomp/lib -lomp

CPPFLAGS += -I/opt/homebrew/opt/libomp/include -Xclang -fopenmp

1. 

curl -O https://mac.r-project.org/openmp/openmp-16.0.4-darwin20-Release.tar.gz

sudo tar fvx openmp-16.0.4-darwin20-Release.tar.gz -C /

This command will put these files in /usr/local/lib and /usr/local/include

You can inspect the downloaded tar.gz file by uncompressing it and see how it is structured. 

2. 

PKG_CPPFLAGS='-Xclang -fopenmp' PKG_LIBS=-lomp R CMD INSTALL /Users/ashish/downloads/data.table-1.15.4.tar.gz 

Just use the above command to install it with flags to detect the openMP install. 

Next time you use the package, it should use multiple threads. Check this under R prompt after loading data.table package:

library(data.table)

getDTthreads()