Assign multiple new variables on LHS in a single line

Question

I want to assign multiple variables in a single line in R. Is it possible to do something like this?

values # initialize some vector of values (a, b) = values[c(2,4)] # assign a and b to values at 2 and 4 indices of 'values' 

Typically I want to assign about 5-6 variables in a single line, instead of having multiple lines. Is there an alternative?

Answer 1

There is a great answer on the Struggling Through Problems Blog

This is taken from there, with very minor modifications.

USING THE FOLLOWING THREE FUNCTIONS (Plus one for allowing for lists of different sizes)

# Generic form '%=%' = function(l, r, ...) UseMethod('%=%')  # Binary Operator '%=%.lbunch' = function(l, r, ...) {   Envir = as.environment(-1)    if (length(r) > length(l))     warning("RHS has more args than LHS. Only first", length(l), "used.")    if (length(l) > length(r))  {     warning("LHS has more args than RHS. RHS will be repeated.")     r <- extendToMatch(r, l)   }    for (II in 1:length(l)) {     do.call('<-', list(l[[II]], r[[II]]), envir=Envir)   } }  # Used if LHS is larger than RHS extendToMatch <- function(source, destin) {   s <- length(source)   d <- length(destin)    # Assume that destin is a length when it is a single number and source is not   if(d==1 && s>1 && !is.null(as.numeric(destin)))     d <- destin    dif <- d - s   if (dif > 0) {     source <- rep(source, ceiling(d/s))[1:d]   }   return (source) }  # Grouping the left hand side g = function(...) {   List = as.list(substitute(list(...)))[-1L]   class(List) = 'lbunch'   return(List) } 

Then to execute:

Group the left hand side using the new function g() The right hand side should be a vector or a list Use the newly-created binary operator %=%

# Example Call;  Note the use of g()  AND  `%=%` #     Right-hand side can be a list or vector g(a, b, c)  %=%  list("hello", 123, list("apples, oranges"))  g(d, e, f) %=%  101:103  # Results:  > a [1] "hello" > b [1] 123 > c [[1]] [1] "apples, oranges"  > d [1] 101 > e [1] 102 > f [1] 103 

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Example using lists of different sizes:

Longer Left Hand Side

g(x, y, z) %=% list("first", "second") #   Warning message: #   In `%=%.lbunch`(g(x, y, z), list("first", "second")) : #     LHS has more args than RHS. RHS will be repeated. > x [1] "first" > y [1] "second" > z [1] "first" 

Longer Right Hand Side

g(j, k) %=% list("first", "second", "third") #   Warning message: #   In `%=%.lbunch`(g(j, k), list("first", "second", "third")) : #     RHS has more args than LHS. Only first2used. > j [1] "first" > k [1] "second" 

Answer 2

Consider using functionality included in base R.

For instance, create a 1 row dataframe (say V) and initialize your variables in it. Now you can assign to multiple variables at once V[,c("a", "b")] <- values[c(2, 4)], call each one by name (V$a), or use many of them at the same time (values[c(5, 6)] <- V[,c("a", "b")]).

If you get lazy and don't want to go around calling variables from the dataframe, you could attach(V) (though I personally don't ever do it).

# Initialize values values <- 1:100  # V for variables V <- data.frame(a=NA, b=NA, c=NA, d=NA, e=NA)  # Assign elements from a vector V[, c("a", "b", "e")] = values[c(2,4, 8)]  # Also other class V[, "d"] <- "R"  # Use your variables V$a V$b V$c  # OOps, NA V$d V$e