How to multiply only one column in an R data frame with a number?

To multiply only one column with a number, we can simply use the multiplication operator * but need to replace the original column with the new values. For example, if we have a data frame called df that contains three columns x1, x2, and x3, and we want to multiply the second column x2 with 2 then it can be done as df$x2<−df$x2*2.

Example1

y1<−rnorm(20)
y2<−rnorm(20)
y3<−rnorm(20)
y4<−rnorm(20)
df2<−data.frame(y1,y2,y3,y4)
df2

Output

y1 y2 y3 y4
1 0.17051839 −1.07371818 0.717652086 −0.6692174
2 0.26654381 −0.82881794 1.144774784 1.0708255
3 1.17587680 −0.03197159 −0.257318856 −0.2734330
4 0.79978274 1.14677652 −1.052941918 0.8212265
5 0.36352605 0.95455643 0.002662389 0.8991729
6 −0.52918622 −1.19824723 1.121770768 −0.1345990
7 −1.30278723 0.90339625 −1.637918585 −0.3986243
8 −2.01380274 −0.61700004 1.319289169 1.4223520
9 −0.10499300 −0.99640769 1.508072921 −0.8711021
10 −0.57019817 0.23396114 0.371342290 −0.5071846
11 −0.92964644 −2.82593133 −0.191162636 0.2482026
12 −0.62824719 1.39458991 −0.250602510 −0.5094344
13 −1.16899182 0.48402510 0.849597620 0.5386604
14 −0.12800221 −1.01570468 −1.370769300 0.3641254
15 1.60649960 1.00993852 −0.181644717 0.7057080
16 −0.09581029 −0.40099838 0.392519844 −1.6369244
17 −0.43375271 −0.29316467 −0.233208374 0.1270293
18 −0.96182839 0.54334525 1.550101688 2.0853380
19 −1.50775746 −0.89573880 0.366389303 0.3372866
20 1.90255916 −1.41836692 0.428073142 −0.1576013

Replacing the column y1 by multiplying the values in it with *1 −

df2$y1<−df2$y1*(−1)
df2

Output

y1 y2 y3 y4
1 −0.17051839 −1.07371818 0.717652086 −0.6692174
2 −0.26654381 −0.82881794 1.144774784 1.0708255
3 −1.17587680 −0.03197159 −0.257318856 −0.2734330
4 −0.79978274 1.14677652 −1.052941918 0.8212265
5 −0.36352605 0.95455643 0.002662389 0.8991729
6 0.52918622 −1.19824723 1.121770768 −0.1345990
7 1.30278723 0.90339625 −1.637918585 −0.3986243
8 2.01380274 −0.61700004 1.319289169 1.4223520
9 0.10499300 −0.99640769 1.508072921 −0.8711021
10 0.57019817 0.23396114 0.371342290 −0.5071846
11 0.92964644 −2.82593133 −0.191162636 0.2482026
12 0.62824719 1.39458991 −0.250602510 −0.5094344
13 1.16899182 0.48402510 0.849597620 0.5386604
14 0.12800221 −1.01570468 −1.370769300 0.3641254
15 −1.60649960 1.00993852 −0.181644717 0.7057080
16 0.09581029 −0.40099838 0.392519844 −1.6369244
17 0.43375271 −0.29316467 −0.233208374 0.1270293
18 0.96182839 0.54334525 1.550101688 2.0853380
19 1.50775746 −0.89573880 0.366389303 0.3372866
20 −1.90255916 −1.41836692 0.428073142 −0.1576013