CODEWITHSUNDEEP
rfor-loop
user9292
user9292

Reputation: 1145

For-loop and storing results in an array in R

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

Upvotes: 1

Views: 1281

Answers (3)

nicola
nicola

Reputation: 24480

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.

Upvotes: 1

akrun
akrun

Reputation: 886948

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)

Upvotes: 3

Colonel Beauvel
Colonel Beauvel

Reputation: 31161

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)

Upvotes: 1

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