Let say I’ve a data frame consists of one variable (x)
df <- data.frame(x=c(1,2,3,3,5,6,7,8,9,9,4,4)) I want to know how many numbers are less than 2,3,4,5,6,7. I know how to do this manually using
# This will tell you how many numbers in df less than 4 xnew <- length(df[ which(df$x < 4), ]) My question is how can I automate this by using for-loop or other method(s)? And I need to store the results in an array as follows
i length 2 1 3 2 4 4 5 6 6 7 7 8 Thanks
One way would be to loop over (sapply) the numbers (2:7), check which elements in df$x is less than (<) the "number" and do the sum, cbind with the numbers, will give the matrix output
res <- cbind(i=2:7, length=sapply(2:7, function(y) sum(df$x <y))) Or you can vectorize by creating a matrix of numbers (2:7) with each number replicated by the number of rows of df, do the logical operation < with df$x. The logical operation is repeated for each column of the matrix, and get the column sums using colSums.
length <- colSums(df$x <matrix(2:7, nrow=nrow(df), ncol=6, byrow=TRUE)) #or #length <- colSums(df$x < `dim<-`(rep(2:7,each=nrow(df)),c(12,6))) cbind(i=2:7, length=length) 
num = c(2,3,4,5,6,7) res = sapply(num, function(u) length(df$x[df$x < u])) data.frame(number=num, numberBelow=res) A vectorized solution:
findInterval(2:7*(1-.Machine$double.eps),sort(df$x)) The .Machine$double.eps part assure that you are taking just the numbers lower than and not lower or equal than.
