find indexes in R by not using `which`

Question

Is there a faster way to search for indices rather than which %in% R.

I am having a statement which I need to execute but its taking a lot of time.

statement:

total_authors<-paper_author$author_id[which(paper_author$paper_id%in%paper_author$paper_id[which(paper_author$author_id%in%data_authors[i])])]

How can this be done in a faster manner?

Are you sure that this indexing is the slow part of your code? — Richie Cotton
– Richie Cotton, Commented Apr 8, 2014 at 11:11
my code is very running very slow and it mainly uses which statements so i thought that it could be due to which statements — user3171906
– user3171906, Commented Apr 8, 2014 at 11:25

Community · Accepted Answer · 2017-05-23 12:21:23Z

1

~~Don't call which. R accepts logical vectors as indices, so the call is superfluous.~~ In light of sgibb's comment, you can keep which if you are sure that you will also get at least one match. (If there are no matches, then which returns an empty vector and you get everything instead of nothing. See Unexpected behavior using -which() in R when the search term is not found.)

Secondly, the code looks a little cleaner if you use with.

Thirdly, I think you want a single index with & rather than a double index.

total_authors <- with(
  paper_author,
  author_id[paper_id %in% paper_id & author_id %in% data_authors[i]
)

edited May 23, 2017 at 12:21

CommunityBot

11 silver badge

answered Apr 8, 2014 at 10:28

Richie Cotton

122k47 gold badges254 silver badges370 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

sgibb Over a year ago

Don't call which is surprisingly not faster than which: stackoverflow.com/questions/17510778/…

hadley Over a year ago

@sgibb it's dangerous to generalised from that one case, and general you should avoid performance optimisation in favour of clear code (unless it's obvious that they reduce a bottleneck)

Collectives™ on Stack Overflow

find indexes in R by not using `which`

1 Answer 1

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Linked

Related