Reputation: 925
Behavior of assignment operators ('=' and '<-') inside a function in R
This is related to Assignment operators in R: '=' and '<-'; however, my question is not answered there.
The linked question and answers explain that using (Ed note: that is not actually stated in the linked answer, and if it were stated, it would be wrong. If you made the statement about the evaluation of argument lists and restricted it to calls of such functions from the global environment it might be correct.)<- inside of a function declares the variable assignment in the user workspace, so that the variable can be used after the function is called.
This would seem to explain the following difference in behavior. This following code produces a data frame exactly as one might expect:
A <- data.frame(
Sub = rep(c(1:3),each=3),
Word = rep(c('Hap','Lap','Sap'),3),
Vowel_Length = sample(c(1:100),9)
)
The result is:
Sub Word Vowel_Length
1 1 Hap 31
2 1 Lap 2
3 1 Sap 71
4 2 Hap 58
5 2 Lap 28
6 2 Sap 20
7 3 Hap 78
8 3 Lap 72
9 3 Sap 77
However, if we use <- inside of the data.frame() function, as follows, we get a different result.
B <- data.frame(
Sub <- rep(c(1:3),each=3),
Word <- rep(c('Hap','Lap','Sap'),3),
Vowel_Length <- sample(c(1:100),9)
)
This result is:
Sub....rep.c.1.3...each...3. Word....rep.c..Hap....Lap....Sap....3.
1 1 Hap
2 1 Lap
3 1 Sap
4 2 Hap
5 2 Lap
6 2 Sap
7 3 Hap
8 3 Lap
9 3 Sap
Vowel_Length....sample.c.1.100...9.
1 31
2 15
3 4
4 2
5 89
6 55
7 12
8 72
9 47
I assume that, because using [See the comments.]<- inside a function declares the variable globally, then the headers of the data frame are inherited from that global declaration, just as the linked question and answers would seem to indicate.
However, I'm curious why you get, for example, Sub....rep.c.1.3...each...3. as the header of the first column in the data frame instead of Sub <- rep(c(1:3),each=3),, or even instead of 1 1 1 2 2 2 3 3 3.
Update:
As @AnandaMahto pointed out in a deleted comment, setting check.names to FALSE produces the following behavior.
C <- data.frame(
Sub <- rep(c(1:3),each=3),
Word <- rep(c('Hap','Lap','Sap'),3),
Vowel_Length <- sample(c(1:100),9),
check.names=FALSE
)
Where the result is:
Sub <- rep(c(1:3), each = 3) Word <- rep(c("Hap", "Lap", "Sap"), 3)
1 1 Hap
2 1 Lap
3 1 Sap
4 2 Hap
5 2 Lap
6 2 Sap
7 3 Hap
8 3 Lap
9 3 Sap
Vowel_Length <- sample(c(1:100), 9)
1 15
2 3
3 82
4 33
5 99
6 53
7 89
8 77
9 47
And to clarify, my question is simply why this behavior is happening. In particular, why do you get Sub....rep.c.1.3...each...3. as a header instead of Sub <- rep(c(1:3),each=3), or 1 1 1 2 2 2 3 3 3 with check.names=TRUE.
And now, I suppose that I'm also curious why you get Sub <- rep(c(1:3),each=3), as the header with check.names=FALSE?
Upvotes: 2
Views: 323
Answers (3)
Reputation: 7374
As other answers point out, you should read what check.names does.
However, you might also consider this:
if you write data.frame( Sub = rep(c(1:3)) ) the equals sign means "bind a named argument called Sub". That named argument stays internal to the call of data.frame().
If you write data.frame( Sub <- rep(c(1:3)) ) the <- sign means "assign into the local environment". So you create a variable called Sub in addition to creating the data.frame. That Sub variable remains present in your environment beyond the lifetime of the data.frame() call.
Upvotes: 0
Reputation: 49448
In the first case you have a named list and in the second an unnamed one. Here's an illustrative example:
f = function(...) {
l = list(...)
print(names(l))
}
f(a = 4, b = 5)
#[1] "a" "b"
f(a <- 4, b <- 5)
#NULL
From that point on, if the list is unnamed, data.frame figures out a naming strategy depending on what check.names is set to.
Upvotes: 3
Reputation: 193687
It appears that your question is about the strange naming that R ends up using, and you're wondering why it doesn't have spaces, <, and so on.
If that's your actual question, you should look at the check.names argument in data.frame.
From ?data.frame:
check.nameslogical. IfTRUEthen the names of the variables in the data frame are checked to ensure that they are syntactically valid variable names and are not duplicated. If necessary they are adjusted (bymake.names) so that they are.
Thus, you can get the names you were expecting by setting check.names to FALSE:
B <- data.frame( Sub <- rep(c(1:3),each=3),
Word <- rep(c('Hap','Lap','Sap'),3),
Vowel_Length <- sample(c(1:100),9),
check.names = FALSE)
B
# Sub <- rep(c(1:3), each = 3) Word <- rep(c("Hap", "Lap", "Sap"), 3)
# 1 1 Hap
# 2 1 Lap
# 3 1 Sap
# 4 2 Hap
# 5 2 Lap
# 6 2 Sap
# 7 3 Hap
# 8 3 Lap
# 9 3 Sap
# Vowel_Length <- sample(c(1:100), 9)
# 1 33
# 2 20
# 3 5
# 4 83
# 5 99
# 6 79
# 7 58
# 8 46
# 9 44
Upvotes: 4
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