zeehio zeehio - 1 month ago 16
R Question

tibble with list columns: Convert to array if possible

I have a tibble as follows:

uuu <- structure(list(IsCharacter = c("a", "b"),
ShouldBeCharacter = list("One", "Another"),
IsList = list("Element1", c("Element2", "Element3"))
),
.Names = c("IsCharacter", "ShouldBeCharacter", "IsList"),
row.names = c(NA, -2L), class = c("tbl_df", "tbl", "data.frame"))
uuu
## A tibble: 2 × 3
# IsCharacter ShouldBeCharacter IsList
# <chr> <list> <list>
#1 a <chr [1]> <chr [1]>
#2 b <chr [1]> <chr [2]>


I would like to convert columns like "ShouldBeCharacter", where all the elements are of the same length and type into a column similar to "IsCharacter", leaving the rest of the columns untouched.

So far I have the following function that solves the problem, but it looks quite hacky to me. I would like to know if there is a better solution I am not considering:

lists_to_atomic <- function(data) {
# Elements of length larger than one should be kept as lists.
# So we compute the maximum length for each column
length_column_elements <- apply(data, 2,
function(x) max(sapply(x, function(y) length(y))))
# to_simplify will contain column names of class list and with all elements of length 1
to_simplify <- colnames(data)[length_column_elements == 1 & sapply(data, class) == "list"]
# Do the conversion
data[,to_simplify] <- tibble::as_tibble(lapply(as.list(data[,to_simplify]), function(x) {do.call(c, x)}))
return(data)
}


Here is the result I obtain, note how the type of ShouldBeCharacter has changed:

lists_to_atomic(uuu)
## A tibble: 2 × 3
# IsCharacter ShouldBeCharacter IsList
# <chr> <chr> <list>
#1 a One <chr [1]>
#2 b Another <chr [2]>


The
as_tibble(lapply(as.list(... do.call(c,...)))
line looks too complex to me but I cannot find a simpler alternative.

Is there any simplification that makes my
lists_to_atomic
function more reliable?

Update



I did not consider using
tidyr::unnest
on columns of type list and elements of length 1, but following @taavi-p answer I have been able to simplify the function to this:

lists_to_atomic <- function(data) {
# Elements of length larger than one should be kept as lists.
# So we compute the maximum length for each column
length_column_elements <- apply(data, 2,
function(x) max(sapply(x, function(y) length(y))))
# to_simplify will contain column names of class list and with all elements of length 1
to_simplify <- colnames(data)[length_column_elements == 1 & sapply(data, class) == "list"]
# Do the conversion
data2 <- tidyr::unnest_(data, unnest_cols = to_simplify)
data2 <- data2[, colnames(data)] # Preserve original column order
return(data2)
}

Answer

You can try:

     library(tidyr)
     uuu %>% unnest(ShouldBeCharacter) 

More examples how to deal with list columns can be found in "R for Data Science": http://r4ds.had.co.nz/many-models.html#list-columns-1

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