Wanting to subtract 1 from several specific columns in a dataframe-CodePudding

I am super new to R, and the many facets of coding language.

I have a set of data with many variables. I have a few columns (that are beside each other), where I need to subtract 1 from all values in those specific columns. Then, I want to replace the values from the original columns ( 1) with the new (-1) values.

CodePudding user response：

One option is use dplyr from tidyverse. I use the function mutate to alter the columns, which I select by using across. Since you have a range of columns that are next to each other, then you can just give the first and last column with : in the middle, which will get all columns in between. Then, I apply a function with ~ to subtract 1 from each value in each column (i.e., .).

Starting Dataframe

  X1 X2 X3 X4 X5 X6 X7 X8
1  3  0  3  8  7  3  2  6
2  1  6 10  1  2  2  5  1
3 10  3  3 10  2  1  6  1
4  7  5  8 10  4  1  3  9
5  4 10  3  7  7  0  0  8

dplyr

library(dplyr)

df %>%
  mutate(across(X2:X7, ~  . - 1))

Output

  X1 X2 X3 X4 X5 X6 X7 X8
1  3 -1  2  7  6  2  1  6
2  1  5  9  0  1  1  4  1
3 10  2  2  9  1  0  5  1
4  7  4  7  9  3  0  2  9
5  4  9  2  6  6 -1 -1  8

Or if you only want to select certain columns, then you can input the names (as I do below) or column index into c().

df %>%
   mutate(across(c(X2, X4, X6), ~  . - 1))

Or if you need to apply the function to every column, then you can use everything().

df %>%
   mutate(across(everything(), ~  . - 1))

The other option as @user20650 provided is to simply use base R and select the columns that you want by index. However, if you want to replace the values in the original dataframe, then you need to assign the new values to the same subset (as @r2evans did above).

df[c(2:7)] <- df[c(2:7)]  - 1

Data

df <-
  structure(
    list(
      X1 = c(3L, 1L, 10L, 7L, 4L),
      X2 = c(0L, 6L, 3L, 5L, 10L),
      X3 = c(3L, 10L, 3L, 8L, 3L),
      X4 = c(8L, 1L, 10L, 10L, 7L),
      X5 = c(7L, 2L, 2L, 4L, 7L),
      X6 = c(3L, 2L, 1L, 1L, 0L),
      X7 = c(2L, 5L, 6L, 3L, 0L),
      X8 = c(6L, 1L, 1L, 9L, 8L)
    ),
    class = "data.frame",
    row.names = c(NA,-5L)
  )

CodePudding user response：

Just subtract 1 from selected columns and assign them back. Really no packages needed.

Example:

df
#   X1 X2 X3 X4
# 1  1  1  1  1
# 2  1  1  1  1
# 3  1  1  1  1

v <- c('X2', 'X4')  ## create vector of column names (or numbers) to change

df[v] <- df[v] - 1  ## subtract and assign back

df  ## result
#   X1 X2 X3 X4
# 1  1  0  1  0
# 2  1  0  1  0
# 3  1  0  1  0

Data:

df <- data.frame(matrix(1, 3, 4))