Add Named Columns to Data Frame in R

Question

I am in the process of reformatting a few data frames and was wondering if there is a more efficient way to add named columns to data frames, rather than the below:

colnames(df) <- c("c1", "c2)

to rename the current columns and:

df$c3 <- ""

to create a new column.

Is there a way to do this in a quicker manner? I'm trying to add dozens of named columns and this seems like an inefficient way of going through the process.

Use the data.tables package. Unlike regular R it modifies its contents in-place and does do the copying to and from a `*tmp*` data-object. — IRTFM, Feb 28 '18 at 20:39
@jogo that second line of code is how I'm creating new blank columns — Franchise, Feb 28 '18 at 20:40
@Franchise But you will fill the column with other values, don't you? Can you show that code? — jogo, Feb 28 '18 at 20:46

score 4 · Answer 1 · answered Feb 28 '18 at 21:13

4

use your method in a shorter way:

cols_2_add=c("a","b","c","f")
 df[,cols_2_add]=""

answered Feb 28 '18 at 21:13

Onyambu

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This is by far the easiest method. – thelatemail Feb 28 '18 at 22:29
Just looked at the comments and saw that you had posted an answer similar to this!! hahaha.. Wow. Thanks – Onyambu Feb 28 '18 at 22:32

MKR · Answer 2 · 2018-03-01T06:38:39.130

A way to add additional columns can be achieved using merge. Apply merge on existing dataframe with the one created with a desired columns and empty rows. This will be helpful if you want to create columns of different types.

For example:

# Existing dataframe
df <- data.frame(x=1:3, y=4:6)

#use merge to create say desired columns as a, b, c, d and e
merge(df, data.frame(a="", b="", c="", d="", e=""))

# Result
#  x y a b c d e
#1 1 4          
#2 2 5          
#3 3 6

# Desired columns of different types
library(dplyr) 
bind_rows(df, data.frame(a=character(), b=numeric(), c=double(), d=integer(),
e=as.Date(character()), stringsAsFactors = FALSE))

#  x y    a  b  c  d    e
#1 1 4 <NA> NA NA NA <NA>
#2 2 5 <NA> NA NA NA <NA>
#3 3 6 <NA> NA NA NA <NA>

score 0 · Answer 3 · answered Feb 28 '18 at 20:40

0

A simple loop can help here

name_list <- c('a1','b1','c1','d1')

# example df
df <- data.frame(a = runif(3))

# this adds a new column
for(i in name_list)
{
    df[[i]] <- runif(3)
}

# output
           a         a1        b1        c1        d1
1 0.09227574 0.08225444 0.4889347 0.2232167 0.8718206
2 0.94361151 0.58554887 0.7095412 0.2886408 0.9803941
3 0.22934864 0.73160433 0.6781607 0.7598064 0.4663031

# in case of data.table, for-set provides faster version:
# example df
df <- data.table(a = runif(3))

for(i in name_list)
    set(df, j=i, value = runif(3))

answered Feb 28 '18 at 20:40

YOLO

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Try your best to avoid loops. Only used when cannot be avoided. Let your goal be **How can I give an Answer with no loops?** – Onyambu Feb 28 '18 at 21:09
Sure thanks! Will keep that in mind. :) – YOLO Feb 28 '18 at 21:28

Add Named Columns to Data Frame in R

3 Answers3