toJSON by row

library(rjson)
library(magrittr)
library(data.table)
library(plyr)
library(dplyr)

toJSON_byRow_1 = function(dat){
  dat %>% alply(1, identity) %>% unname %>% toJSON %>% cat
}

toJSON_byRow_2 = function(dat){
  dat %>% apply(1, function(x){
      x[sapply(x, class) == "character"] %<>% paste0("\"", ., "\"")
      x[sapply(x, class) == "factor"] %<>% paste0("\"", as.character(.), "\"")
      paste0(paste0("\"", names(x), "\":"), x) %>%
        paste(collapse = ",") %>% paste0("{", ., "}")
    }) %>% paste(.,collapse=",\n") %>%
    paste0("[", ., "]") %>% cat()
}

toJSON_byRow_3 = function(dat){
  check.numeric <- function(x){
    all(regexpr("^\\d*\\.?\\d*$", as.character(x)) > 0)
  }

  dat %<>% sapply(check.numeric) %>% which() %>%
    names() %>% paste0(., "=as.numeric(", ., ")") %>%
    {within(dat, eval(parse(text=.)))}

  dat %>% mutate(splitter = 1:nrow(.)) %>%
    plyr:::splitter_d(.(splitter)) %>% llply(select, -splitter) %>%
    llply(toJSON) %>% do.call(c, .) %>%
    paste0(collapse = ",\n") %>% paste0("[\n", ., "\n]\n") %>% cat()
}

jsonFile = "[{\"speed\":4,\"dist\":2,\"brand\":\"Audi\"},
  {\"speed\":4,\"dist\":10,\"brand\":\"Benz\"},
  {\"speed\":7,\"dist\":4,\"brand\":\"Audi\"},
  {\"speed\":7,\"dist\":22,\"brand\":\"Benz\"},
  {\"speed\":8,\"dist\":16,\"brand\":\"Benz\"}
]"

dat = fromJSON(jsonFile) %>% unlist() %>% cbind(names(.)) %>%
  data.table() %>% setnames(paste0("X", 1:2)) %>%
  plyr:::splitter_d(.(X2)) %>% laply(function(x){
    x[,1]
  }) %>% t() %>% data.table()


toJSON_byRow_1(dat)
# [{"brand":"Audi","dist":"2","speed":"4"},{"brand":"Benz","dist":"10","speed":"4"},{"brand":"Audi","dist":"4","speed":"7"},{"brand":"Benz","dist":"22","speed":"7"},{"brand":"Benz","dist":"16","speed":"8"}]
toJSON_byRow_2(dat)
# [{"brand":"Audi","dist":"2","speed":"4"},
# {"brand":"Benz","dist":"10","speed":"4"},
# {"brand":"Audi","dist":"4","speed":"7"},
# {"brand":"Benz","dist":"22","speed":"7"},
# {"brand":"Benz","dist":"16","speed":"8"}]
toJSON_byRow_3(dat)
# [
# {"brand":"Audi","dist":2,"speed":4},
# {"brand":"Benz","dist":10,"speed":4},
# {"brand":"Audi","dist":4,"speed":7},
# {"brand":"Benz","dist":22,"speed":7},
# {"brand":"Benz","dist":16,"speed":8}
# ]