Create vector of data frame names from a list of data frames

Question

I have a list of data frames, and I want to create a character vector that contains the data frame names that meet a certain criteria. In this case, I want the names of the data frames that contain at least 1 observation. I need these names in a vector for use in another function later on.

The list of data frames is created automatically by the split function. For reproducibility, here's a list of data frames:

df1 <- data.frame(replicate(2,sample(0:1,5,rep=TRUE)))
df2 <- data.frame(replicate(2,sample(0:1,5,rep=TRUE)))
df3 <- data.frame(replicate(0,sample(0:1,5,rep=TRUE))) #empty

mylist <- list(df1, df2,df3) #create list of data frames

mylist2 <- mylist[sapply(mylist, function(x) dim(x)[1]) > 0] #subset list so that df's with no observations are dropped

Now, what I need is a character vector with the names of the data frames in mylist2. (In this example, "df1" and "df2".)

Thanks!

Possible duplicate of stackoverflow.com/questions/44944307/… — akrun
– akrun, Commented Jul 6, 2017 at 15:48

agenis - code en bois · Accepted Answer · 2017-07-06 15:49:29Z

3

If you want this to be somewhat automatized, for instance you have a large number of data.frames in your environment, you might want to select them with a pattern matching in one line:

mylist = do.call("list", mget(grep("df", ls(), value=T)))
mylist2 <- mylist[sapply(mylist, function(x) dim(x)[1]) > 0]

This creates the first list with all data.frames that have "df" in their names, while keeping their names as attributes of the list elements.

Then I apply your filter for 1-element data.frames and you just retrieve the names:

names(mylist2)
#### [1] "df1" "df2"

answered Jul 6, 2017 at 15:49

agenis - code en bois

8,4177 gold badges60 silver badges110 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

lmo Over a year ago

Your second and third line are equivalent to names(mylist)[sapply(mylist, nrow) > 0].

Perry Kuipers · Accepted Answer · 2017-07-06 15:42:26Z

2

You need to have a named list. Here is how you could do it:

library(dplyr)
library(purrr)

mylist <- list(df1 = df1, df2 = df2, df3 = df3)

test <- mylist %>%
  map_int(nrow)

test[test > 0] %>% names()
#[1] "df1" "df2"

answered Jul 6, 2017 at 15:42

Perry Kuipers

1216 bronze badges

2 Comments

user3780463 Over a year ago

Thanks! The issue is that I have over 250 data frames. Is there a simple way to assign each data frame a name without having type out "df1 = df1....df250 = df250"? (I realize this is out of the scope of the original question but a quick search yields no helpful results.)

Perry Kuipers Over a year ago

If the list has already been created then you could do: names(mylist) <- paste0("df", 1L:length(mylist))

Collectives™ on Stack Overflow

Create vector of data frame names from a list of data frames

2 Answers 2

1 Comment

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related