在R中将多列转换为Json数组？

Question

Say I have the mtcars dataset, and I wanted to take three columns and turn them into a JSON array. How do I convert this to a json array and is that possible to pass them into a POSTGRESQL database?

library(jsonlite)
df <- mtcars
attach(mtcars)
json.column <- cbind(mpg,cyl,disp) 

Do I use toJSON() ?

mtcars.json <- toJSON(json.column)

https://cran.r-project.org/web/packages/jsonlite/vignettes/json-aaquickstart.html

Array of objects [{"name":"Erik", "age":43}, {"name":"Anna", "age":32}] Data Frame simplifyDataFrame

Answer 1

Keep your data as a data.frame, not a matrix. Use

json.column <- data.frame(mpg,cyl,disp)
toJSON(json.column)
# [{"mpg":21,"cyl":6,"disp":160},{"mpg":21,"cyl":6,"disp":160}, ...

Also, you should avoid the use of attach() . It can cause lots of problems if you forget detach() . Plus you can use with() often to avoid it

json.column <- with(mtcars, data.frame(mpg,cyl,disp))

Answer 2

(For starters, never use attach ! It's dangerous! Use with instead, typically.)

There are a bunch of ways to do it. Here's how to create the values using dplyr:

qq <- rowwise(mtcars) %>% 
    mutate(newcol=as.character(jsonlite::toJSON(list(mpg=mpg, cyl=cyl, disp=disp))))
> qq$newcol
 [1] "{\"mpg\":[21],\"cyl\":[6],\"disp\":[160]}"     "{\"mpg\":[21],\"cyl\":[6],\"disp\":[160]}"    
 [3] "{\"mpg\":[22.8],\"cyl\":[4],\"disp\":[108]}"   "{\"mpg\":[21.4],\"cyl\":[6],\"disp\":[258]}"  
 ...

From there, if your Postgres database is set up with newcol as a JSON type, I think just writing that table as usual should work.