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create list of vectors in for loop

4 messages · Jim Lemon, Paul Sanfilippo, Peter Dalgaard

Original
Paul Sanfilippo
# 
Hi,

As an exercise, I am trying to create a list of 10 random number vectors in a loop. I can create the vectors but am unsure how to assemble them in the list as part of the loop. Any advice?


# Number of vectors to create
n <- c(1:10)

# Create empty list to store vectors
list_of_vecs <- list()

# Create n vectors of random numbers - length 10. This works ok.
for (i in seq_along(n)){
? assign(paste('vec_', i, sep = ''), rnorm(10,0,1))
}

# But how do I append them in a list. This doesn?t work:
for (i in seq_along(n)){
? list_of_vecs <- list(list_of_vecs,(assign(paste('vec_', i, sep = ''), rnorm(10,0,1))))
}


Thank you,

Paul
Jim Lemon
# 
Hi Paul,
The easy to understand way is:

n <- c(1:10)
# Create empty list to store vectors
list_of_vecs <- list()

# Create n vectors of random numbers - length 10. This works ok.
for (i in n){
 list_of_vecs[[i]]<-rnorm(10,0,1)
}

If you really want to use "assign":
for (i in n){
 vecname<-paste('vec_', i, sep = '')
 assign(vecname, rnorm(10,0,1))
 list_of_vecs[[i]]<-get(vecname)
}

Jim
On Tue, Dec 6, 2016 at 8:44 PM, Paul Sanfilippo <prseye at gmail.com> wrote:
Paul Sanfilippo
# 
Thank you Jim.
On 6 December 2016 at 9:17:21 pm, Jim Lemon (drjimlemon at gmail.com) wrote:
Hi Paul,  
The easy to understand way is:  

n <- c(1:10)  
# Create empty list to store vectors  
list_of_vecs <- list()  

# Create n vectors of random numbers - length 10. This works ok.  
for (i in n){  
list_of_vecs[[i]]<-rnorm(10,0,1)  
}  

If you really want to use "assign":  
for (i in n){  
vecname<-paste('vec_', i, sep = '')  
assign(vecname, rnorm(10,0,1))  
list_of_vecs[[i]]<-get(vecname)  
}  

Jim
On Tue, Dec 6, 2016 at 8:44 PM, Paul Sanfilippo <prseye at gmail.com> wrote:

  
  


  


      

    

    

      
      

        


  

        

      Peter Dalgaard
    

    

      
      #
    

  


  

      
On 06 Dec 2016, at 11:17 , Jim Lemon <drjimlemon at gmail.com> wrote:

        

            

      
      
      
    

        
As a principle, you want 

  list_of_vecs <- vector("list", 10)

to avoid extending the list on each iteration.


However, a simpler way is

replicate(10, rnorm(10), simplify=FALSE)

(where the simplify bit prevents conversion to 10x10 matrix)

or 

lapply(1:10, function(i) rnorm(10))