No problem! Let's break down how to replicate that MATLAB logic in R.

First, a quick recap: In MATLAB, isfield(opt, 'TolKKT') checks if the struct opt has a field named TolKKT. The code sets a default value of 0.001 if that field doesn't exist.

In R, we typically use lists to mimic MATLAB's structs (since they support named key-value pairs). Here are two reliable ways to replicate the isfield check:

1. Use hasName() (R 3.4.0+) #

This is the most direct and readable equivalent, designed specifically to check if a named object has a given name:

# Check if "TolKKT" is not present, then set default
if (!hasName(opt, "TolKKT")) {
  opt$TolKKT <- 0.001
}

2. Use %in% with names() (compatible with all R versions) #

If you need to support older R versions where hasName() isn't available, use this more universal approach:

# Check if "TolKKT" isn't in the list of names for opt
if (!("TolKKT" %in% names(opt))) {
  opt$TolKKT <- 0.001
}

Example in action #

Let's say your opt list starts without the TolKKT field:

opt <- list(MaxIter = 100, TolFun = 1e-6)

Running either of the above code blocks will add TolKKT = 0.001 to your opt list, just like the MATLAB original does.

内容的提问来源于stack exchange，提问作者nickolakis