If I have the following object
[1] 0 1 0 0 0 0 0 0 0
How do I convert it to this so that I can put it in one column and it aligns with my other columns in my data frame:
0
1
0
0
0
0
0
I thought list might work...but which function should this work on
So sorry for asking a suppose to be basic question...
If you have a data.frame say, "DF", like this:
DF <- data.frame(x=1:9, y=letters[1:9])
And you've a vector z:
z <- c(0, 1, 0, 0, 0, 0, 0, 0, 0)
Note that the number of rows in your data.frame and the length of the vector has to be the same if you want to add the vector to a data.frame as a new column.
dim(DF) # dimensions of data.frame
# [1] 9 2
length(z) # length of vector
# [1] 9
Now, you can use cbind to get the new column as follows:
cbind(DF, z)
# x y z
# 1 1 a 0
# 2 2 b 1
# 3 3 c 0
# 4 4 d 0
# 5 5 e 0
# 6 6 f 0
# 7 7 g 0
# 8 8 h 0
# 9 9 i 0
If you have a vector whose length is not equal to that of the data.frame rows, then,
z <- c(0, 1, 0, 0, 0, 0, 0) # length is 7
cbind(DF, z)
# Error in data.frame(..., check.names = FALSE) :
# arguments imply differing number of rows: 9, 7
cbind'ing results in error due to unequal lengths. In this case, I could think of a couple ways to store this as a list.
First, you can keep your data.frame DF as such and create a list with its first element as the data.frame and the second as a vector as follows:
my_l <- list(d1 = DF, d2 = z)
# $d1
# x y
# 1 1 a
# 2 2 b
# 3 3 c
# 4 4 d
# 5 5 e
# 6 6 f
# 7 7 g
# 8 8 h
# 9 9 i
#
# $d2
# [1] 0 1 0 0 0 0 0
Alternatively, you can convert your data.frame to a list (a data.frame is internally a list) and create a list whose elements are all vectors as follows:
my_l <- c(as.list(DF), list(z=z))
# $x
# [1] 1 2 3 4 5 6 7 8 9
#
# $y
# [1] a b c d e f g h i
# Levels: a b c d e f g h i
#
# $z
# [1] 0 1 0 0 0 0 0
Note that as.list coerces a data.frame columns to a list with it's names the column names of the data.frame. We then create a new list z and then concatenate using the c operator.
Hope this betters your understanding a bit.
In addition to Aruns great and detailed answer, there are two things worth noting:
First, R recycles shorter items to match the length of the longer items. In the case of adding a vector to a data.frame, this will only occur if the number of rows of the data.frame is an exact multiple of the length of the vector.
zshort <- c(1, 2, 3)
# will be `0` if exact multiple:
length(zshort) %/% nrow(DF)
# [1] 0
cbind(DF, zshort)
# cbind(DF, zshort)
# x y zshort
# 1 a 1
# 2 b 2
# 3 c 3
# 4 d 1 <~~ Recycling
# 5 e 2
# 6 f 3
# 7 g 1 <~~ Recycling
# 8 h 2
# 9 i 3
(2) You can also add a new column to a data.frame using "[" as follows:
# name of the column does NOT have to be
# the same as the name of the vector
DF[, "newName"] <- z
DF[, "shortz"] <- zshort
# You can also delete existing columns
DF[, "y"] <- NULL
DF
# x newName shortz
# 1 1 1
# 2 2 2
# 3 3 3
# 4 1 1
# 5 2 2
# 6 3 3
# 7 1 1
# 8 2 2
# 9 3 3