Index of the first occurence of each value in a vector

Question

I have a vector and I want to get the location (indices) of the first occurrence of each unique value.

vec <- c(4,4,4,3,3,3,5,4,5,4,3,3,56)
(pos <- ?????????)

I want in return

# 1  4  7  13

I.e. 1 is the first index of 4, 4 is the first index of 3, and so on.

See `?duplicated`; `which(!duplicated(vec))` – alexis_laz Mar 18 '16 at 12:27 — alexis_laz, Mar 18 '16 at 12:27
@alexis_laz Thats the answer i want to accept – Coolwater Mar 20 '16 at 10:21 — Coolwater, Mar 20 '16 at 10:21

Ronak Shah · Accepted Answer · 2016-03-18T12:25:47.447

6

Similar to @Pratik's approach

You can use match along with unique

match(unique(vec), vec)

#[1]  1  4  7 13

edited Mar 18 '16 at 12:25

answered Mar 18 '16 at 12:20

Ronak Shah

355,584
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score 2 · Answer 2 · answered Mar 18 '16 at 12:06

2

The following code should do the trick for you:

vec <- c(4,4,4,3,3,3,5,4,5,4,3,3,56)

firstUniqueOccurrence <- function(vec) {
    unq <- unique(vec)
    sapply(unq, function(x) {min(which(vec == x))})
}

firstUniqueOccurrence(vec)

[1]  1  4  7 13

answered Mar 18 '16 at 12:06

Sergey Bushmanov

19,458
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60

score 2 · Answer 3 · answered Mar 18 '16 at 12:11

2

As per you your vector element, try using below command to get the desired output.

match(c(4,3,5,56), vec)

answered Mar 18 '16 at 12:11

Index of the first occurence of each value in a vector

3 Answers3

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