CODEWITHSUNDEEP
r
123123123
123123123

Reputation: 31

for loop with "<-" to create variables in R

So I have this data :

data<-as.data.frame(matrix(1:9,ncol=3))

which gives this :

| V1 | V2 | V3 |  
________________  
|  1 | 2  | 3  | 
|  4 | 5  | 6  |
|  7 | 8  | 9  |

I want to create a variable for each column to get this :

> V1
[1] 1 2 3

> V2
[1] 4 5 6

> V3
[1] 7 8 9

I know that if I do a loop with the assign function :

for (i in 1:length(data)) {
               assign(names(data[i]),data[,i])
               
}

it works. But if I try with the "<-" :

for (i in 1:length(data)) {
           names(data[i])<-data[,i]
           
}

it does not work. Why does it work with the assign function but not with the "<-" ?

Upvotes: 2

Views: 75

Answers (2)

SteveM
SteveM

Reputation: 2301

You can also use lapply to keep your vectors as a list. (Easier to reference):

nrows <- nrow(data)
nrows
3
vecs <- lapply(1:nrows, function(x) data[x, ])
vecs
[[1]]
  V1 V2 V3
1  1  4  7

[[2]]
  V1 V2 V3
2  2  5  8

[[3]]
  V1 V2 V3
3  3  6  9

Upvotes: 1

akrun
akrun

Reputation: 887158

We can use list2env

list2env(data, .GlobalEnv)

-check for objects

V1
#[1] 1 2 3
V2
#[1] 4 5 6
V3
#[1] 7 8 9

In the for loop, it can be looped over the column names and use assign

for(nm in names(data)) assign(nm, data[[nm]])

The names assignment works only for assigning the column names or names attribute of a vector and not create an object. The error is basically about the difference in length of the lhs and rhs of the assignment (<-) operator

names(data[1])
#[1] "V1"

Better would be

names(data)[1]

and

data[,1]
#[1] 1 2 3

is the value of the column which is of length 3

when we assign <-) it to the names(data)[1], it is assigning the first column name to 1 2 3 which differs in length

names(data)[1] <- data[,1]

Warning message: In names(data)[1] <- data[, 1] : number of items to replace is not a multiple of replacement length

returns a warning, but if we use the OP's method of subsetting

names(data[1]) <- data[,1]

Error in names(data[1]) <- data[, 1] : 'names' attribute [3] must be the same length as the vector [1]

Upvotes: 1

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