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Vectorized code: calculating a log-sum

A common operation in statistics is to calculate the sum of log probabilities. The following code calculates the log-sum (the sum of the logs).

# x is a vector of probabilities
total <- 0
for(i in seq_along(x)) 
    total <- total + log(x[i])

However this piece of code could be significantly improved using vectorized code.

This exercise is part of the course

Writing Efficient R Code

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Exercise instructions

  • Find the log-sum of x using the log() and sum() functions, simplify the above loop.
  • Store your answer in the object log_sum.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

# Initial code
n <- 100
total <- 0
x <- runif(n)
for(i in 1:n) 
    total <- total + log(x[i])

# Rewrite in a single line. Store the result in log_sum
log_sum <- ___
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