keep

Keep or drop symbols

Keep or drop symbols

Usage

keep(a, yes)
discard(a, no)

Note

Function keep() needs an explicit return() to prevent it from returning invisibly.

The functions are vectorised in the first argument but not the second.

The second argument---the symbols to keep or discard---is formally a vector of nonnegative integers, but the functions coerce it to a free object. The symbols kept or dropped are the union of the symbols in the elements of the vector. Function discard() was formerly known as drop() but this conflicted with base::drop().

These functions have nothing in common with APL's take() and drop().

Aliases

• keep
• discard
• drop
• drop.free

Examples

# NOT RUN {
x <- rfree(10,5,8)

keep(x,abc(4))           # keep only symbols a,b,c,d
discard(x,as.free('cde'))   # drop symbols c,d,e



x[1:4] %<>% keep(alpha(3))  # keep only abc in first 4 elements of x



# }