Flatten nested data frames

In a nested data frame, one or more of the columns consist of another data frame. These structures frequently appear when parsing JSON data from the web. We can flatten such data frames into a regular 2 dimensional tabular structure.

flatten(x, recursive = TRUE)

Arguments

x	a data frame
recursive	flatten recursively

Examples

options(stringsAsFactors=FALSE)
x <- data.frame(driver = c("Bowser", "Peach"), occupation = c("Koopa", "Princess"))
x$vehicle <- data.frame(model = c("Piranha Prowler", "Royal Racer"))
x$vehicle$stats <- data.frame(speed = c(55, 34), weight = c(67, 24), drift = c(35, 32))
str(x)
#> 'data.frame':	2 obs. of  3 variables:
#>  $ driver    : chr  "Bowser" "Peach"
#>  $ occupation: chr  "Koopa" "Princess"
#>  $ vehicle   :'data.frame':	2 obs. of  2 variables:
#>   ..$ model: chr  "Piranha Prowler" "Royal Racer"
#>   ..$ stats:'data.frame':	2 obs. of  3 variables:
#>   .. ..$ speed : num  55 34
#>   .. ..$ weight: num  67 24
#>   .. ..$ drift : num  35 32
str(flatten(x))
#> 'data.frame':	2 obs. of  6 variables:
#>  $ driver              : chr  "Bowser" "Peach"
#>  $ occupation          : chr  "Koopa" "Princess"
#>  $ vehicle.model       : chr  "Piranha Prowler" "Royal Racer"
#>  $ vehicle.stats.speed : num  55 34
#>  $ vehicle.stats.weight: num  67 24
#>  $ vehicle.stats.drift : num  35 32
str(flatten(x, recursive = FALSE))
#> 'data.frame':	2 obs. of  4 variables:
#>  $ driver       : chr  "Bowser" "Peach"
#>  $ occupation   : chr  "Koopa" "Princess"
#>  $ vehicle.model: chr  "Piranha Prowler" "Royal Racer"
#>  $ vehicle.stats:'data.frame':	2 obs. of  3 variables:
#>   ..$ speed : num  55 34
#>   ..$ weight: num  67 24
#>   ..$ drift : num  35 32

if (FALSE) {
data1 <- fromJSON("https://api.github.com/users/hadley/repos")
colnames(data1)
colnames(data1$owner)
colnames(flatten(data1))

# or for short:
data2 <- fromJSON("https://api.github.com/users/hadley/repos", flatten = TRUE)
colnames(data2)
}