R: append a "character" type to a list of numeric values

Question

I have a list of numeric values, say

> list <- c(1,10,12,24)
> list
[1]  1 10 12 24

and I want to append a string of characters to it so that the output reads:

> list
[1]  "name" 1 10 12 24

I tried the following code:

list <- c("name",1,10,12,24)

or

list <- c(1,10,12,24)
list <- c("name",as.numeric(list))

but, predictably, all the numerics were converted to a character type:

> list <- c(1,10,12,24)
> list <- c("name",as.numeric(list))
> list
[1] "name" "1"    "10"   "12"   "24"

How can I preserve the numeric type while adding a character type in front?

[EDIT] The goal is to add this as a row to an existing data frame df where df[1] contains strings and df[2:5] contain numerics.

Solution 1

@Fernando pretty much has the idea right: your "row" should be a list if you want to combine it with a data.frame.

Here are a couple of examples:

## A sample `data.frame`
mydf <- data.frame(A = c("one", "two"), B = 1:2, C = 3:4, 
                   D = 5:6, stringsAsFactors = FALSE)

## Your initial vector...
addMe <- c(1, 10, 12)
## ... now as a list
addMe <- c("name", as.list(addMe))
addMe
# [[1]]
# [1] "name"
# 
# [[2]]
# [1] 1
# 
# [[3]]
# [1] 10
#
# [[4]]
# [1] 12
#

## Put it all together...
new <- rbind(mydf, addMe)
new
#      A B  C  D
# 1  one 1  3  5
# 2  two 2  4  6
# 3 name 1 10 12
str(new)
# 'data.frame':  3 obs. of  4 variables:
#  $ A: chr  "one" "two" "name"
#  $ B: num  1 2 1
#  $ C: num  3 4 10
#  $ D: num  5 6 12

---

Alternatively, create a one row (or more, if necessary) data.frame and bind that with the existing data.frame:

addMe <- c(1, 10, 12)
rbind(mydf, setNames(cbind("name", data.frame(t(addMe))), names(mydf)))
#      A B  C  D
# 1  one 1  3  5
# 2  two 2  4  6
# 3 name 1 10 12 

---

Major note: This depends on your first column being a character, not factor, variable. If they are factors, you need to make sure the variable contains the right levels (or convert to character first, then re-factor).

Solution 2

How about using the list element name for the string:

l <- list('name'=c(1,10,12,24))
l
## $name
## [1]  1 10 12 24

names(l)
## [1] "name"

Extract the numeric vector by name:

l[["name"]]
## [1]  1 10 12 24

Make this into a data frame:

as.data.frame(l)
##   name
## 1    1
## 2   10
## 3   12
## 4   24

Solution 3

You' using a vector, not a list. You cannot mix types in vectors, use a list instead:

my.list = list(1,10,12,24)
my.list = append("name", my.list)

And remember that 'growing' structures in R is very bad for performance.

Comments

[Matthew Lundberg]

You want to create a vector that contains a string and numerics. That's not possible. How about using the list element name?

[Roland]

Why do you want this? There's probably a much better alternative.

[biohazard]

I want to add this as a new row in a data frame, where the first column are names and the other columns contain numerics...

[Matthew Lundberg]

@biohazard Then you want to name the elements of the list, not add a name to the vector.

[Matthew Lundberg]

Given the question's latest edit, I'm not sure that this really answers the question.

[biohazard]

That's right, I wasn't able to append it as a row to my data frame (even by using t(as.data.frame(l))... so I gave up and added the row by hand in the raw data and re-imported it ^^; but your answer still taught me something!

[A5C1D2H2I1M1N2O1R2T1]

+1. The problem pretty much boils down to this issue. It would have been nice to see a more fleshed out answer though.