How to get the name of a data.frame within a list?
Question
How can I get a data frame's name from a list? Sure, get()
gets the object itself, but I want to have its name for use within another function. Here's the use case, in case you would rather suggest a work around:
lapply(somelistOfDataframes, function(X) {
ddply(X, .(idx, bynameofX), summarise, checkSum = sum(value))
})
There is a column in each data frame that goes by the same name as the data frame within the list. How can I get this name bynameofX
? names(X)
would return the whole vector.
EDIT: Here's a reproducible example:
df1 <- data.frame(value = rnorm(100), cat = c(rep(1,50),
rep(2,50)), idx = rep(letters[1:4],25))
df2 <- data.frame(value = rnorm(100,8), cat2 = c(rep(1,50),
rep(2,50)), idx = rep(letters[1:4],25))
mylist <- list(cat = df1, cat2 = df2)
lapply(mylist, head, 5)
Solution
I'd use the names of the list in this fashion:
dat1 = data.frame()
dat2 = data.frame()
l = list(dat1 = dat1, dat2 = dat2)
> str(l)
List of 2
$ dat1:'data.frame': 0 obs. of 0 variables
$ dat2:'data.frame': 0 obs. of 0 variables
and then use lapply + ddply like:
lapply(names(l), function(x) {
ddply(l[[x]], c("idx", x), summarise,checkSum = sum(value))
})
This remains untested without a reproducible answer. But it should help you in the right direction.
EDIT (ran2): Here's the code using the reproducible example.
l <- lapply(names(mylist), function(x) {
ddply(mylist[[x]], c("idx", x), summarise,checkSum = sum(value))
})
names(l) <- names(mylist); l
OTHER TIPS
Here is the dplyr equivalent
library(dplyr)
catalog =
data_frame(
data = someListOfDataframes,
cat = names(someListOfDataframes)) %>%
rowwise %>%
mutate(
renamed =
data %>%
rename_(.dots =
cat %>%
as.name %>%
list %>%
setNames("cat")) %>%
list)
catalog$renamed %>%
bind_rows(.id = "number") %>%
group_by(number, idx, cat) %>%
summarize(checkSum = sum(value))
you could just firstly use names(list)->list_name and then use list_name[1] , list_name[2] etc. to get each list name. (you may also need as.numeric(list_name[x]) if your list names are numbers.