# counts numbers in a interval

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Say I have a list of values, and I cut them by some break points, how do I know the number of values in each interval?**One Tip Per Day**, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

We know cut() function in R works for the purpose. For example,

tx0 <- c(9, 4, 6, 5, 3, 10, 5, 3, 5) x <- rep(0:8, tx0) > x [1] 0 0 0 0 0 0 0 0 0 1 1 1 1 2 2 2 2 2 2 3 3 3 3 3 4 4 4 5 5 5 5 5 5 5 5 5 5 6 [39] 6 6 6 6 7 7 7 8 8 8 8 8 > table( cut(x, b = 8)) (-0.008,0.994] (0.994,2] (2,3] (3,4] (4,5] 9 4 6 5 13 (5,6] (6,7.01] (7.01,8.01] 5 3 5In the cut() document, there is a note, saying

Instead of table(cut(x, br)), hist(x, br, plot = FALSE) is more efficient and less memory hungry. Instead of cut(*, labels = FALSE), findInterval() is more efficient. But if you try as it said, you will the counts returned look different: > hist(x, 8, plot=F) $breaks [1] 0 1 2 3 4 5 6 7 8 $counts [1] 13 6 5 3 10 5 3 5 What's wrong? Nothing is wrong. Just missed argument. "When breaks is specified as a single number, the range of the data is divided into breaks pieces of equal length, and then the outer limits are moved away by 0.1% of the range to ensure that the extreme values both fall within the break intervals. (If x is a constant vector, equal-length intervals are created, one of which includes the single value.)" The conclusion is: when breaks is a vector, table( cut(x, b = 0:8,include.lowest = T)) is equal to hist(x, breaks=0:8, plot=F)$counts; when breaks is a single number, it's not.

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