Thank you Bert for this clarification. It is indeed an important point.
Ivan
--
Ivan Calandra, PhD
Scientific Mediator
University of Reims Champagne-Ardenne
GEGENAA - EA 3795
CREA - 2 esplanade Roland Garros
51100 Reims, France
+33(0)3 26 77 36 89
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Le 23/06/2016 à 17:06, Bert Gunter a écrit :
Sorry, Ivan, your statement is incorrect:
"When you use a single bracket on a list with only one argument in
between, then R extracts "elements", i.e. columns in the case of a
data.frame. This explains your errors. "
e.g.
ex <- data.frame(a = 1:3, b = letters[1:3])
a <- 1:3
identical(ex[1], a)
[1] FALSE
class(ex[1])
[1] "data.frame"
class(a)
[1] "integer"
Compare:
identical(ex[[1]], a)
[1] TRUE
Why? Single bracket extraction on a list results in a list; double
bracket extraction results in the element of the list ( a "column" in
the case of a data frame, which is a specific kind of list). The
relevant sections of ?Extract are:
"Indexing by [ is similar to atomic vectors and selects a **list** of
the specified element(s).
Both [[ and $ select a **single element of the list**. "
Hope this clarifies this often-confused issue.
Cheers,
Bert
Bert Gunter
"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
On Thu, Jun 23, 2016 at 7:34 AM, Ivan Calandra
<ivan.calan...@univ-reims.fr> wrote:
My statement "Using a single bracket '[' on a data.frame does the same as
for matrices: you need to specify rows and columns" was not correct.
When you use a single bracket on a list with only one argument in between,
then R extracts "elements", i.e. columns in the case of a data.frame. This
explains your errors.
But it is possible to use a single bracket on a data.frame with 2 arguments
(rows, columns) separated by a comma, as with matrices. This is the solution
you received.
Ivan
--
Ivan Calandra, PhD
Scientific Mediator
University of Reims Champagne-Ardenne
GEGENAA - EA 3795
CREA - 2 esplanade Roland Garros
51100 Reims, France
+33(0)3 26 77 36 89
ivan.calan...@univ-reims.fr
--
https://www.researchgate.net/profile/Ivan_Calandra
https://publons.com/author/705639/
Le 23/06/2016 à 16:27, Ivan Calandra a écrit :
Dear Georg,
You need to learn a bit more about the subsetting methods, depending on
the object structure you're trying to subset.
More specifically, when you run this: ds_test[is.na(ds_test$var1)]
you get this error: "Error in `[.data.frame`(ds_test, is.na(ds_test$var1))
: undefined columns selected"
This means that R does not understand which column you're trying to
select. But you're actually trying to select rows.
Using a single bracket '[' on a data.frame does the same as for matrices:
you need to specify rows and columns, like this:
ds_test[is.na(ds_test$var1), ] ## notice the last comma
ds_test[is.na(ds_test$var1), ] <- 0 ## works on all columns because you
didn't specify any after the comma
If you want it only for "var1", then you need to specify the column:
ds_test[is.na(ds_test$var1), "var1"] <- 0
It's the same problem with your 2nd and 4th tries (4th one has other
problems). Your 3rd try does not change ds_test at all.
HTH,
Ivan
--
Ivan Calandra, PhD
Scientific Mediator
University of Reims Champagne-Ardenne
GEGENAA - EA 3795
CREA - 2 esplanade Roland Garros
51100 Reims, France
+33(0)3 26 77 36 89
ivan.calan...@univ-reims.fr
--
https://www.researchgate.net/profile/Ivan_Calandra
https://publons.com/author/705639/
Le 23/06/2016 à 15:57, g.maub...@weinwolf.de a écrit :
Hi All,
I would like to recode my NAs to 0. Using a single vector everything is
fine.
But if I use a data.frame things go wrong:
-- cut --
var1 <- c(1:3, NA, 5:7, NA, 9:10)
var2 <- c(1:3, NA, 5:7, NA, 9:10)
ds_test <-
data.frame(var1, var2)
test <- var1
test[is.na(test)] <- 0
test # NA recoded OK
# First try
ds_test[is.na(ds_test$var1)] <- 0 # duplicate subscripts WRONG
# Second try
ds_test[is.na("var1")] <- 0
ds_test$var1 # not recoded WRONG
# Third try: to me the most intuitive approach
is.na(ds_test["var1"]) <- 0 # attempt to select less than one element in
integerOneIndex WRONG
# Fourth try
ds_test[is.na(var1)] <- 0 # duplicate subscripts for columns WRONG
-- cut --
How can I do it correctly?
Where could I have found something about it?
Kind regards
Georg
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