Replace the subsetted and modified data back into the main dataframe-CodePudding

I have a data frame with 20 rows, I randomly select n rows and modify them. How can I put the modified value back to the original data frame with only the modified value being different?

df<- data.frame(rnorm(n = 20, mean = 0, sd = 1))
n = 8
a<- data.frame(df[ c(1, sample(2:(nrow(df)-1), n), nrow(df) ), ])
a$changedvalue <- a[,1]*(2.5)

Now I want to replace the values of the original dataframe df with the values of a$changedvalue such that only the sampled values are changed while everything else is same in df. I tried doing something like this but it's not working.

df %>% a[order(as.numeric(rownames(a))),]

I just want to point out that in my original dataset the data are timeseries data, so maybe they can be used for the purpose.

CodePudding user response：

Instead of writing data.frame(df[ c(1, sample(2:(nrow(df)-1), n), nrow(df) ), ])

You can define the rows you want to use, lets call it rows

rows <- c(1, sample(2:(nrow(df)-1), n), nrow(df) )

Now you can do

a<- data.frame(df[rows, ])
a$changedvalue <- a[,1]*(2.5)

df[rows, ] <- a$changedvalue