search among rows of matrix and return values from column in R

user_11763233 0
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In R, I have a matrix M of the form

lower upper value 
0.1   0.2  1.2 
0.2   0.3  2.4
0.3   0.4 -0.3

And a vector v with values in (0,1). For each value in v, I want to find the corresponding row in M such that the value is between the 'lower' and 'upper' values in that row, and get the corresponding number from the value column. The output should be a vector y of the same length as v where each element of y is the relevant 'value' as described above. How should I do this? I know I need to use the apply function but can't think of the most efficient way.

For example: For the M above, suppose v = c(0.12, 0.34). Then the expected output is y = c(1.2, -0.3)

apply r
3 Answers

Another option is to use sapply to pull value that fits the condition from v.

sapply(v, \(x) M[x > M[, "lower"] & x < M[, "upper"],][["value"]])

#[1]  1.2 -0.3

Data

M <- structure(c(0.1, 0.2, 0.3, 0.2, 0.3, 0.4, 1.2, 2.4, -0.3), .Dim = c(3L, 
3L), .Dimnames = list(NULL, c("lower", "upper", "value")))

v = c(0.12, 0.34)
user_152931910 
M[findInterval(v, c(M[1,'lower'], M[,'upper'])), 'value']
[1]  1.2 -0.3
user_83802720

Use cut with each of the v values to find which range it falls into:

# example data for `v`:
set.seed(1)
v <- round(runif(5, min=0.1, max=0.4),2)
#[1] 0.18 0.21 0.27 0.37 0.16

M[, "value"][cut(v, c(M[1, "lower"], M[, "upper"]))]
#[1]  1.2  2.4  2.4 -0.3  1.2

Where M was:

M <- as.matrix(read.table(text="lower upper value 
0.1   0.2  1.2 
0.2   0.3  2.4
0.3   0.4 -0.3",  header=TRUE))
user_4968030
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