for (i in 1:length(lastname)){
        x <- gsub(x, pattern = paste0("\b", lastname[i], "\b", sep = ""), replacement = "<LASTNAME>")
}

# Function to make the grouped pattern
groupPat <- function(pat0, ng)
{
    # pat0: original list of patterns
    # ng: number of original patterns in one group
    # pat1: new, grouped pattern

    # Length of original pattern
    np0 <- length(pat0)

    # Length of pattern to make
    np1 <- floor(np0/ng)

    if (np1 > 0){
        # Allocate memory
        pat1 <- vector(mode = "list", length = np1)

        # Make new pattern
        for (i in 1:np1-1){
            pat1[i] <- paste0("\b", pat0[(i*ng+1):((i+1)*ng)], "\b", collapse = "|")
        }
        pat1[np1] <- paste0("\b", pat0[(np1*ng+1):np0], "\b", collapse = "|")
    } else {
        pat1 <- paste0("\b", pat0, "\b", collapse = "|")
    }

    # Output
    pat1
}


# The actual replacement loop:
pat <- groupPat(lastname, 100)
for (i in 1:length(pat)){
    x <- gsub(x, pattern = pat[i], replacement = "LASTNAME")
}