copy value from last row and paste in to first row r

Question

I have a dataframe. In it the values in col3 and col4 are in the wrong row by 1. The bottom row values are supposed to be in the top row, the top row should be in the second and so on

Currently

col1 col2  col3  col4
 a    b      c     d
 e     f     g     h
 i      j    k     l

should be

 col1 col2  col3  col4
  a    b      k     l
  e     f     c     d
   i    j     g     h

how do I move just the values in col3 and col4 by one down with the last becoming the first?

Answer 1

I tend to use dplyr's mutate_each and summarise_each functions to apply the same function(s) to multiple columns. Here's how you could approach it with a custom "swap" function for better readability:

library(dplyr)

Define a function:

swap <- function(x) c(last(x), head(x, -1L))

Now you can use this custom function inside "mutate_each" and specify the columns you want to apply the function to:

mutate_each(df, funs(swap), col3, col4)
#  col1 col2 col3 col4
#1    a    b    k    l
#2    e    f    c    d
#3    i    j    g    h

---

If you prefer base R, you could do it similarly, using a slightly modified function "swap2" and "lapply" to apply the function to multiple columns:

# define the function:
swap2 <- function(x) c(tail(x, 1L), head(x, -1L))
# define the columns you want to apply the function to:
cols <- c("col3", "col4")
# Finally, lapply over the data:
df[cols] <- lapply(df[cols], swap2)

data:

> dput(df)
structure(list(col1 = c("a", "e", "i"), col2 = c("b", "f", "j"
), col3 = c("c", "g", "k"), col4 = c("d", "h", "l")), .Names = c("col1", 
"col2", "col3", "col4"), class = "data.frame", row.names = c(NA, 
-3L))

Answer 2

Assume d is your data.frame:

d$col3 <- c(d$col3[length(d$col3)], d$col3[-length(d$col3)])
d$col4 <- c(d$col4[length(d$col4)], d$col4[-length(d$col4)])

Answer 3

Try this

df <- data.frame(col1=c("a", "e", "i"),
                 col2=c("b", "f", "j"),
                 col3=c("c", "g", "k"),
                 col4=c("d", "h", "l"))


df <- cbind(df[, 1:2], df[c(dim(df)[1], 1:(dim(df)[1]-1)), 3:4])

Answer 4

Create the data frame using characters rather than factors:

df <- data.frame(col1=c("a", "e", "i"),
                 col2=c("b", "f", "j"),
                 col3=c("c", "g", "k"),
                 col4=c("d", "h", "l"), stringsAsFactors=FALSE)

df$col3 <- c(df$col3[nrow(df)], df$col3[1:(nrow(df)-1)])
df$col4 <- c(df$col4[nrow(df)], df$col4[1:(nrow(df)-1)])

Output:

> df
  col1 col2 col3 col4
1    a    b    k    l
2    e    f    c    d
3    i    j    g    h

Answer 5

Assuming that df is your dataframe, you can use a for loop

temp3 = df[nrow(df),3]
temp4 = df[nrow(df),4]
for(i in 2:nrow(df)){
    df[(i,3] = df[((i - 1),3]
    df[(i,4] = df[((i - 1),4]
}
df[1, 3] = temp3
df[1, 4] = temp4