Create multiple variables in a loop

Question

Is there a way to create multiple variables in a loop. For example, if I have a variable, called 'test' among others, in my data frame, how can I create a series of new variables called say 'test1', 'test2', ... 'testn' that are defined as test^1, test^2... test^n

As an example

mynum <- 1:10
myletters <- letters[1:10]
mydf <- data.frame(mynum, myletters)

mydf
   mynum myletters
1      1         a
2      2         b
3      3         c
4      4         d
5      5         e
6      6         f
7      7         g
8      8         h
9      9         i
10    10         j

for (i in 1:5)
    {paste0(var, i) <- mynum^i
    }

But it errors out.

I am trying to create variables like var1, var2, var3 etc which are mynum^1, mynum^2, mynum^3 etc.

Best regards

Deepak

Ronak Shah · Accepted Answer · 2020-09-11 00:54:06Z

You can use lapply to create new columns and combine them using do.call + cbind.

n <- 1:5
mydf[paste0('var', n)] <- do.call(cbind, lapply(n, function(x) mydf$mynum^x))
mydf

#   mynum myletters var1 var2 var3  var4   var5
#1      1         a    1    1    1     1      1
#2      2         b    2    4    8    16     32
#3      3         c    3    9   27    81    243
#4      4         d    4   16   64   256   1024
#5      5         e    5   25  125   625   3125
#6      6         f    6   36  216  1296   7776
#7      7         g    7   49  343  2401  16807
#8      8         h    8   64  512  4096  32768
#9      9         i    9   81  729  6561  59049
#10    10         j   10  100 1000 10000 100000

Or with purrr's map_dfc

mydf[paste0('var', n)] <- purrr::map_dfc(n, ~mydf$mynum^.x)

Duck · Accepted Answer · 2020-09-11 00:39:59Z

Try this, you have to take into account that you have to move the position of the new variables. That is why I use i+2 in the loop. Here the code:

#Data
mynum <- 1:10
myletters <- letters[1:10]
mydf <- data.frame(mynum, myletters,stringsAsFactors = F)

The loop:

#Loop
for (i in 1:5)
{
  mydf[,i+2]  <- mydf[,'mynum']^i
  names(mydf)[i+2] <- paste0('var',i)
}

Output:

   mynum myletters var1 var2 var3  var4   var5
1      1         a    1    1    1     1      1
2      2         b    2    4    8    16     32
3      3         c    3    9   27    81    243
4      4         d    4   16   64   256   1024
5      5         e    5   25  125   625   3125
6      6         f    6   36  216  1296   7776
7      7         g    7   49  343  2401  16807
8      8         h    8   64  512  4096  32768
9      9         i    9   81  729  6561  59049
10    10         j   10  100 1000 10000 100000

Oh, thank you! This was exactly what I was looking for. Seems simple after you see the answer, isn't it?
@DeepakAgarwal Yes, it is like a matrix. If you feel this answer was useful, you could accept it by ticking the click on the left side of this answer. It is up to you :)

akrun · Accepted Answer · 2020-09-11 16:46:10Z

1

An option with map

library(dplyr)
library(purrr)
map_dfc(1:5, ~ mydf$mynum^.x) %>% 
                 rename_all(~ str_replace(., '\\.+', 'var')) %>% 
                 bind_cols(mydf, .)

answered Sep 11, 2020 at 16:46

akrun

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