Create a new column in R based on the content of another column [specific case]

Question

I am looking for a smart way to modify my data.set. If I manage to do that will save a lot of time

my data set looks like this

column1 
1.0
1.0
2.0
2.0.15
0.0
1.0.30

and I would like to create a new "parental column" where I keep the first part of column 1

column1  column2
1.0        1
1.0        1
2.0        2
2.0.15     2.0
0.0        0
1.0.30     1.0

The reason I want to do that is that I want to recreate a parent-offspring relationship among elements. Column 2 is supposed to be the parents and column 1 its offspring. Any help is highly appreciated.

Answer 1

One option using the tidyverse and regex:

library(tidyverse)

orig <- tribble(
  ~column1, 
  "1.0",
  "1.0",
  "2.0",
  "2.0.15",
  "0.0",
  "1.0.30"
)

orig
#> # A tibble: 6 x 1
#>   column1
#>   <chr>  
#> 1 1.0    
#> 2 1.0    
#> 3 2.0    
#> 4 2.0.15 
#> 5 0.0    
#> 6 1.0.30

orig %>% 
  mutate(parent = str_replace(column1, "\\.\\d+$", ""))
#> # A tibble: 6 x 2
#>   column1 parent
#>   <chr>   <chr> 
#> 1 1.0     1     
#> 2 1.0     1     
#> 3 2.0     2     
#> 4 2.0.15  2.0   
#> 5 0.0     0     
#> 6 1.0.30  1.0

^{Created on 2020-08-05 by the reprex package (v0.3.0)}

The regex \\.\\d+$ takes a literal dot . followed by one or more digits, followed by the end of the string $ and replaces this match with nothing "" . See also https://regexr.com/59lnl (where the end of line $ is replaced with a newline \n ).

Answer 2

Try this:

#Data
df <- structure(list(column1 = c("1.0", "1.0", "2.0", "2.0.15", "0.0", 
"1.0.30")), row.names = c(NA, -6L), class = "data.frame")
#Code
#Create column
df$column2 <- sub("^(.*)[.].*", "\\1", df$column1)

Output:

  column1 column2
1     1.0       1
2     1.0       1
3     2.0       2
4  2.0.15     2.0
5     0.0       0
6  1.0.30     1.0

Answer 3

df$column2 <- sub("\\.[0-9]+$", "", df$column1)
df
#   column1 column2
# 1     1.0       1
# 2     1.0       1
# 3     2.0       2
# 4  2.0.15     2.0
# 5     0.0       0
# 6  1.0.30     1.0

Data

df <- data.frame(column1 = c("1.0", "1.0", "2.0", "2.0.15", "0.0", "1.0.30"))