xx_comm_which: Global Which Functions

In pbdMPI: R Interface to MPI for HPC Clusters (Programming with Big Data Project)

Global Which Functions

Description

These functions are global which, which.max and which.min applying on distributed data for all ranks.

Usage

comm.which(x, arr.ind = FALSE, useNames = TRUE,
           comm = .pbd_env$SPMD.CT$comm)
comm.which.max(x, comm = .pbd_env$SPMD.CT$comm)
comm.which.min(x, comm = .pbd_env$SPMD.CT$comm)

Arguments

x	a 'logical' vector or array as in which(), or an 'numeric' objects in which.max() and which.min().
arr.ind	logical, as in which().
useNames	logical, as in which().
comm	a communicator number.

Details

These functions will apply which(), which.max() and which.min() locally, and apply allgather() to get all local results from other ranks.

Value

The global values (which(), which.max(), or which.min()) are returned to all ranks.

comm.which() returns with two columns, 'rank id' and 'index of TRUE'.

comm.which.max() and comm.which.min() return with three values, 'the _smallest_ rank id', 'index of the _first_ maximum or minimum', and 'max/min value of x'.

Author(s)

Wei-Chen Chen [e-mail], George Ostrouchov, Drew Schmidt, Pragneshkumar Patel, and Hao Yu.

References

Programming with Big Data in R Website: https://pbdr.org/

See Also

comm.read.table()

Examples

## Not run: 
### Save code in a file "demo.r" and run with 2 processors by
### SHELL> mpiexec -np 2 Rscript demo.r

spmd.code <- "
### Initialize
suppressMessages(library(pbdMPI, quietly = TRUE))

if(comm.size() != 2){
  comm.cat(\"2 processors are requried.\n\", quiet = TRUE)
  finalize()
}

### Examples.
a <- 1:(comm.rank() + 1)

b <- comm.which(a == 2)
comm.print(b)
b <- comm.which.max(a)
comm.print(b)
b <- comm.which.min(a)
comm.print(b)

### Finish.
finalize()
"
# execmpi(spmd.code, nranks = 2L)

## End(Not run)

pbdMPI documentation built on Aug. 30, 2025, 1:12 a.m.