CODEWITHSUNDEEP
rdataframe
Anne
Anne

Reputation: 387

Shift values in single column of dataframe up

Using example data like this:

example=data.frame(x=c(1,2,3,4,5,6,7,8), y=c(1,2,3,4,5,6,7,8), z=c(1,2,3,4,5,6,7,8))

which looks like this: 

    x   y   z
1   1   1   1
2   2   2   2
3   3   3   3
4   4   4   4
5   5   5   5
6   6   6   6
7   7   7   7
8   8   8   8

I would like to shift all values in the z column upwards by two rows while the rest of the dataframe remains unchanged. The result should look like this:

    x   y   z
1   1   1   3
2   2   2   4
3   3   3   5
4   4   4   6
5   5   5   7
6   6   6   8
7   7   7   NA
8   8   8   NA

I only found ways to move the values of a column down, or a shifting of the whole dataframe.

Any ideas? Thanks!

Upvotes: 18

Views: 36313

Answers (5)

Nicholas Munu
Nicholas Munu

Reputation: 1

## In case you want to shift your rows down by one step for only one column
`z <- example$'z'`

# Deleting the last z value in order to shift values 
# ahead by one period to realign with other rows

z_1 <-head(z,-1)

# We set the initial z value to zero

for (i in 1: (length(z)+1)) {
  if(i != 1){
    z[i] = Z_1[i-1]}
  else{
    z[i] = 0
  }
}
Z
# Append Z to dataframe
example$z <- z

Upvotes: 0

adamsipos
adamsipos

Reputation: 51

This function in the 'useful' package moves columns in both direction: https://www.rdocumentation.org/packages/useful/versions/1.2.6/topics/shift.column

Upvotes: -2

Nettle
Nettle

Reputation: 3321

example = tibble(x=c(1,2,3,4,5,6,7,8), 
                   y=c(1,2,3,4,5,6,7,8), 
                   z=c(1,2,3,4,5,6,7,8))

example %>% mutate_at(c("z"), funs(lead), n = 2 )

# A tibble: 8 x 3
      x     y     z
  <dbl> <dbl> <dbl>
1  1.00  1.00  3.00
2  2.00  2.00  4.00
3  3.00  3.00  5.00
4  4.00  4.00  6.00
5  5.00  5.00  7.00
6  6.00  6.00  8.00
7  7.00  7.00 NA   
8  8.00  8.00 NA

Upvotes: 10

David Arenburg
David Arenburg

Reputation: 92292

I couldn't find a good duplicate, so here's another solution using length<-

shift2 <- function(x, n) `length<-`(tail(x, -n), length(x)) 
# or just shift2 <- function(x, n) c(tail(x, -n), rep(NA, n))
transform(example, z = shift2(z, 2))   
#   x y  z
# 1 1 1  3
# 2 2 2  4
# 3 3 3  5
# 4 4 4  6
# 5 5 5  7
# 6 6 6  8
# 7 7 7 NA
# 8 8 8 NA

Upvotes: 2

Andrie
Andrie

Reputation: 179428

Your problem simplifies to:

  • Drop the first n elements in a vector
  • Pad n values of NA at the end

You can do this with a simple function:

shift <- function(x, n){
  c(x[-(seq(n))], rep(NA, n))
}

example$z <- shift(example$z, 2)

The result:

example
  x y  z
1 1 1  3
2 2 2  4
3 3 3  5
4 4 4  6
5 5 5  7
6 6 6  8
7 7 7 NA
8 8 8 NA

Upvotes: 20

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