How to rearrange columns in some rows in Rstudio?

Question

I'm new to R and have a problem with manipulating data in R. I combined multiple excel files and then separate a string column into multiple string columns. I found that the contents in original columns are not in the same order. How can I select some specific rows to work with and then rearrange some columns in specific rows into the correct order?

The example of dataframe as shown below. I would like to rearrange row#4 and row#5.
Thank you very much.

> a <- c("I", "You", "We", "eat", "eat")
> b <- c("eat", "eat", "eat", "They", "We")
> df <- data.frame(a, b)       
> df

> df
    a    b
1   I  eat
2 You  eat
3  We  eat
4 eat They
5 eat   We  

Answer 1

Try this,we can use transform function

a <- c("I", "You", "We", "eat", "eat")
b <- c("eat", "eat", "eat", "They", "We")
df <- data.frame(a, b)      
df<-rbind(df[1:3,],transform(df[4:5,],a=b,b=a))

 output
     a   b
1    I eat
2  You eat
3   We eat
4 They eat
5   We eat