Calculating row sums

The second bottleneck identified was calculating the row sums.

total <- apply(d, 1, sum)

In the previous exercise you switched the underlying object to a matrix. This makes the above apply operation three times faster. But there's one further optimization you can use - switch apply() with rowSums().

Complete the r_sum() function using rowSums().
Use the microbenchmark() function to compare the timings of app() and r_sum().

Take Hint (-30 XP)

Exercise

Calculating row sums

Instructions