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

If you want the position of all occurrences of a value in a vector, use:

vec <- c("a", "b", "c", "b", "a")
which(vec == "b")

This returns the indices of every "b" in the vector.

Using match()
If you only need the first match’s index:

match("b", vec)

This returns the index of the first "b" and ignores subsequent matches.

Pro Tips

• which() returns all matching positions as a numeric vector.
• match() returns the position of the first match, or NA if not found.
• If multiple values are specified, match() can handle a vector of search terms, returning the first match for each.

Further Learning
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• Grokking the Coding Interview: Patterns for Coding Questions to master pattern-based problem solving.
• Grokking Data Structures & Algorithms for Coding Interviews for robust algorithmic foundations.
• Grokking System Design Fundamentals if you’re aiming to build or analyze scalable systems.

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