Get the Index of the Values of One Vector in Another

Get the index of the values of one vector in another?

Getting indexes of values is what match() is for.

 first = c( "a" , "c" , "b" )
 second = c( "c" , "b" , "a" )
 match(second, first)
 [1] 2 3 1

How to find indices of element in one vector in other vector R

a <-  c('Q1', 'Q2', 'Q3')
b <- c('Q10', 'Q13', 'Q1', 'Q1', 'Q40', 'Q2', 'Q2', 'Q2')

which(b %in% a)

[1] 3 4 6 7 8

Position of elements from one vector in another vector with R

You are looking for pmatch:

a <- c(1,1,2,2,3,3,4,4,5,5)
b <- c(1,2,3,4,5)
pmatch(b,a)
#[1] 1 3 5 7 9

a <- c(1,1,2,2,3,3,4,4,5,5)
b <- c(1,2,2,3,4,5)
pmatch(b,a)
#[1] 1 3 4 5 7 9

a <- c(1,1,2,2,3,3,4,4,5,5)
b <- c(1,2,2,3,4,4,5)
pmatch(b,a)
#[1] 1 3 4 5 7 8 9

a <- c(1,1,2,2,3,3,4,4,5,5)
b <- c(1,2,2,3,4,4,5,5)
pmatch(b,a)
#[1]  1  3  4  5  7  8  9 10

a <- c(1,1,2,2,3,3,4,4,5,5)
b <- c(1,1,2,2,3,4,4,5,5)
pmatch(b,a)
#[1]  1  2  3  4  5  7  8  9 10

a <- c(1,1,2,2,3,3,4,4,5,5)
b <- c(1,1,2,2,3,3,4,4,5,5)
pmatch(b,a)
# [1]  1  2  3  4  5  6  7  8  9 10

index from one vector to another by closest values

You can use findInterval, which constructs a sequence of intervals given by breakpoints in b and returns the interval indices in which the elements of a are located (see also ?findInterval for additional arguments, such as behavior at interval boundaries).

a = 1:20
b = seq(from = 1, to = 20, by = 5)

findInterval(a, b)
#>  [1] 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4

Get indexes of a vector of numbers in another vector

Using base R you could do the following:

v <- c(2,2,3,5,8,0,32,1,3,12,5,2,3,5,8,33,1)
x <- c(2,3,5,8)

idx <- which(v == x[1])
idx[sapply(idx, function(i) all(v[i:(i+(length(x)-1))] == x))]
# [1]  2 12

This tells you that the exact sequence appears twice, starting at positions 2 and 12 of your vector v.

It first checks the possible starting positions, i.e. where v equals the first value of x and then loops through these positions to check if the values after these positions also equal the other values of x.

Finding the index values for a combination of vectors

Both conditions define logical vectors so AND them and get which indices they correspond to. Then plot.

I have added color to make the text labels more obvious.

max_hat <- boxplot.stats(hat, coef = 2)$stats[5]

i <- abs(rs) > 1.96  # abs() because +/-1.96 are 
                     # symmetric values
j <- hat > max_hat
k <- which(i & j)

plot(hat, rs, cex = 0.2+3*sqrt(x), pch = 19)
text(hat[k], rs[k], labels = names(k), pos = 2, col = "red")

Finding index of vector from two other vectors

Using literally logical operators gives the boolean hin2. Then just replace the negation with NA.

hin2 <- m2 %in% 1 | (m2 %in% 2 & d2 %in% 2)
# [1]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE
# [13] FALSE FALSE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE
h2new <- replace(h2, !hin2, NA)
# [1]  1  2  3  4  5  1  2  3  4  5 NA NA NA NA NA  1  2  3  4  5

To select the values, do:

h_new <- h2[!is.na(h2new)]
# [1] 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

Use values of one vector as index range for another vector

You can try:

tapply(vec2, rep(seq_along(vec1), vec1), mean)
#tapply(vec2, unlist(Map(rep, seq_along(vec1), each=vec1)), mean) #Alternative
#tapply(vec2, inverse.rle(list(lengths=vec1, values=seq_along(vec1))), mean) #Alternative
#        1         2         3         4         5         6         7         8 
#0.8674819 0.4983137 0.6256578 0.7409621 0.5225631 0.2523873 0.7349288 0.9176322 
#        9        10        11        12        13        14 
#0.7887523 0.5765066 0.3077164 0.1463103 0.9065303 0.1076056 

Is there an R function for finding the index of an element in a vector?

The function match works on vectors:

x <- sample(1:10)
x
# [1]  4  5  9  3  8  1  6 10  7  2
match(c(4,8),x)
# [1] 1 5

match only returns the first encounter of a match, as you requested. It returns the position in the second argument of the values in the first argument.

For multiple matching, %in% is the way to go:

x <- sample(1:4,10,replace=TRUE)
x
# [1] 3 4 3 3 2 3 1 1 2 2
which(x %in% c(2,4))
# [1]  2  5  9 10

%in% returns a logical vector as long as the first argument, with a TRUE if that value can be found in the second argument and a FALSE otherwise.

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