CODEWITHSUNDEEP
rstata
stata
stata

Reputation: 533

How to count the number of observations in R like Stata command count

aaa<- data.frame(sex=c(1,1,2,2,1,1), group1=c(1,2,1,2,2,2),group2=c("A","B","A","B","A","B"))

stata command:

count if sex==1 & group1==2
count if sex==1 & group2=="A"

count counts the number of observations that satisfy the specified conditions. If no conditions are specified, count displays the number of observations in the data.

How to count in R? Thank you.

Upvotes: 11

Views: 198734

Answers (2)

Nikos Tavoularis
Nikos Tavoularis

Reputation: 2913

You can also use the filter function from the dplyr package which returns rows with matching conditions.

> library(dplyr)

> nrow(filter(aaa, sex == 1 & group1 == 2))
[1] 3
> nrow(filter(aaa, sex == 1 & group2 == "A"))
[1] 2

Upvotes: 4

hrbrmstr
hrbrmstr

Reputation: 78832

The with function will let you use shorthand column references and sum will count TRUE results from the expression(s).

sum(with(aaa, sex==1 & group1==2))
## [1] 3

sum(with(aaa, sex==1 & group2=="A"))
## [1] 2

As @mnel pointed out, you can also do:

nrow(aaa[aaa$sex==1 & aaa$group1==2,])
## [1] 3

nrow(aaa[aaa$sex==1 & aaa$group2=="A",])
## [1] 2

The benefit of that is that you can do:

nrow(aaa)
## [1] 6

And, the behaviour matches Stata's count almost exactly (syntax notwithstanding).

Upvotes: 14

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