loop in loop creating a vector in R

Question

I would like to create a vector using names and numbers.

I have 2 groups : A and B. I have 2 genders: male and female I have 2 animals: dog and cat

Instead of writing a vector containting the name of each group:

vector= c("Amaledog","Afemaledog","Amalecat","Afemalecat","Bmaledog","Bfemaledog","Bmalecat","Bfemalecat")

I would like to use loop in loop:

group=c("A","B")
gender=c("female","male")
animal=c("dog","cat")

for (a in group){
 for (b in gender){
  for (c in animal){
   vector=paste0(a,b,c)
  }
 }
}

But I only obtain : "Bmalecat"

Do you know why? How can I fix this problem?

Please mark one of the answers below as correct, if any worked for you. — prateek1592
– prateek1592, Commented Sep 15, 2016 at 11:21

prateek1592 · Accepted Answer · 2016-09-15 11:16:43Z

4

You could just use expand.grid

expand.grid(group=c("A","B"),gender=c("female","male"),animal=c("dog","cat"))

Output :

  group gender animal
1     A female    dog
2     B female    dog
3     A   male    dog
4     B   male    dog
5     A female    cat
6     B female    cat
7     A   male    cat
8     B   male    cat

Edit :

do.call(paste0, expand.grid(group=c("A","B"),gender=c("female","male"),animal=c("dog","cat")))

This should do it, as pointed out in the comments.

edited Sep 15, 2016 at 11:16

answered Sep 15, 2016 at 11:12

prateek1592

5476 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Roland Over a year ago

do.call(paste0, expand.grid(group, gender, animal))

Mily Over a year ago

thank you for you answer. I want to have one vector containing the names and not a data :)

prateek1592 Over a year ago

Edited the answer, using Roland's advice

Roland · Accepted Answer · 2016-09-15 11:20:18Z

1

You overwrite vector each time, that's the problem. What you probably want to do is

vect <- character(length(group) * length(gender) * length(animal))

i <- 1
for (a in group){
  for (b in gender){
    for (c in animal){
      vect[i] <- paste0(a,b,c)
      i <- i + 1
    }
  }
}

It's important to preallocate the vector in order to avoid a hell lot of (inefficient) reallocation. You should preferably use a vectorised solution.

edited Sep 15, 2016 at 11:20

Roland

134k12 gold badges203 silver badges305 bronze badges

answered Sep 15, 2016 at 11:12

Eli Korvigo

10.5k6 gold badges50 silver badges75 bronze badges

3 Comments

Roland Over a year ago

I feel like a broken record: "Do not grow an object in a loop. At least pre-allocate to the final size." vect <- character(length(group) * length(gender) * length(animal))

Eli Korvigo Over a year ago

@Roland that's precisely what I told myself

Mily Over a year ago

Thank you Eli Korvigo and Roland for your answers.It will work for me. Have a nice day.

akrun · Accepted Answer · 2016-09-15 13:27:34Z

0

Here is an option using data.table with the cross join (CJ)

library(data.table)
CJ(group, gender, animal)[, do.call(paste0, .SD)]
#[1] "Afemalecat" "Afemaledog" "Amalecat"   "Amaledog"   "Bfemalecat"
#[6] "Bfemaledog" "Bmalecat"   "Bmaledog"

answered Sep 15, 2016 at 13:27

akrun

891k38 gold badges590 silver badges700 bronze badges

Collectives™ on Stack Overflow

loop in loop creating a vector in R

3 Answers 3

3 Comments

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related