How to Convert values to the share of sum of row in dataframe in R?

How can I convert the value of each row to the share sum of row?
For instance

df <- data.frame (year  = c("2015", "2016", "2017","2018","2019"),
                  var1 = c(45,45,34,89,55),
                  var2 = c(15,44,33,81,51),
                  var3 = c(12,43,14,29,15)
                  )

  year var1 var2 var3
1 2015   45   15   12
2 2016   45   44   43
3 2017   34   33   14
4 2018   89   81   29
5 2019   55   51   15

Here 45 should be changed by 45/(45 +15+12)*100 and so on for the whole data frame?

>Solution :

You can divide each column by rowSums()

df[,-1] <- df[,-1]*100/rowSums(df[,-1])

Output:

  year     var1     var2     var3
1 2015 62.50000 20.83333 16.66667
2 2016 34.09091 33.33333 32.57576
3 2017 41.97531 40.74074 17.28395
4 2018 44.72362 40.70352 14.57286
5 2019 45.45455 42.14876 12.39669

Here is a similar approach using mutate(across()) from dplyr

library(dplyr)
mutate(df, across(-year, ~.x*100/rowSums(df[,-1])))