Zip or enumerate in R?

Question

What are the R equivalents for these Python list comprehensions:

[(i,j) for i,j in zip(index, Values)] [(i,j) for i,j in enumerate(Values)] [(i,j) for i,j in enumerate(range(10,20))]   %MWE, indexing or enumerating to                                              %keep up with the index, there may                                              %be some parameter to look this up 

Example with Output

>>> [(i,j) for i,j in enumerate(range(10,20))] [(0, 10), (1, 11), (2, 12), (3, 13), (4, 14), (5, 15), (6, 16), (7, 17), (8, 18), (9, 19)] 

I have solved this problem earlier with some trick in R but cannot remember anymore, the first idea was itertools -pkg but I am hoping to find a more idiomatic way of doing things.

Answer 1

Answer for python enumerate:

In R, a list is ordered (see this answer). Thus, all you need is to index either keys (using names()[i]) or values (using [[i]]).

Using seq_along (alternatively can do for(i in 1:length(mylist)){...}):

> mylist <- list('a'=10,'b'=20,'c'=30) > for (i in seq_along(mylist)){ +   print(paste(i,names(mylist)[i],mylist[[i]])) + } [1] "1 a 10" [1] "2 b 20" [1] "3 c 30" 

Answer for python zip:

See one of the above answers to mimic the list of tuples. My preference is towards a data frame as shown in BondedDust's answer:

> x <- 1:3 > y <- 4:6 > data.frame(x=x, y=y)   x y 1 1 4 2 2 5 3 3 6 

Answer 2

There have been some discussions around list comprehension for R, e.g. here or there. The hash package even offers dictionary-like structure. However, as others said, it is difficult to try to map one language facilities onto another (even if this is what Comparison of programming languages actually offers) without a clear understanding of what it is supposed to be used to. For example, I can mimic Python zip() in R as follows:

Python

In [1]: x = [1,2,3] In [2]: y = [4,5,6] In [3]: zip(x, y) Out[3]: [(1, 4), (2, 5), (3, 6)] 

R

> x <- 1:3 > y <- 4:6 > list(x, y)                     # gives a simple list > as.list(paste(x, y))           # three tuples, as a list of characters > mapply(list, x, y, SIMPLIFY=F) # gives a list of 3 tuples > rbind(x, y)                    # gives a 2x3 matrix  

As can be seen, this really depends on what you want to do with the result afterwards.