CODEWITHSUNDEEP
r
phill
phill

Reputation: 95

Filter character vector based on first two elements

I have a vector that look like this:

data <- c("0115", "0159", "0256", "0211")

I want to filter the data based on the first 2 elements of my vector. For example:

group 1 - elements that start with 01

group 2 - elements that start with 02

Any idea how to accomplish this?

Upvotes: 2

Views: 3687

Answers (1)

Simon Jackson
Simon Jackson

Reputation: 3174

You might want to use Regular Expression (regex) to find strings that start with "01" or "02".

Base approach is use grep(), which returns indices of strings that match a pattern. Here's an example - notice I've changed the 2nd and 4th data elements to demonstrate how just searching for "01" or "02" will lead to incorrect answer:

d <- c("0115", "0102", "0256", "0201")

grep("01", d)
#> [1] 1 2 4

d[grep("01", d)]
#> [1] "0115" "0102" "0201"

Because this searches for "01" anywhere, you get "0201" in the mix. To avoid, add "^" to the pattern to specify that the string starts with "01":

grep("^01", d)
#> [1] 1 2

d[grep("^01", d)]
#> [1] "0115" "0102"

If you use the stringr package, you can also use str_detect() in the same way:

library(stringr)

d[str_detect(d, "^01")]
#> [1] "0115" "0102"

Upvotes: 3

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