如何将 JSON 导入 R 并将其转换为表格？

Question

我想使用现在以 JSON 格式保存的数据。但我对 R 很陌生，对如何处理数据一无所知。您可以在下面看到我设法实现的目标。但首先，我的代码：

library(rjson)
json_file <- "C:\\Users\\Saonkfas\\Desktop\\WOWPAPI\\wowpfinaljson.json"
json_data <- fromJSON(paste(readLines(json_file), collapse=""))

我能够得到数据：

for (x in json_data){print (x)}

虽然输出看起来很原始：

[[1]]
[[1]]$wins
[1] "118"

[[1]]$losses
[1] "40"
# And so on

请注意，JSON 有点嵌套。我可以用 Python 创建表，但 R 似乎要复杂得多。

编辑：

我的 JSON：

{
"play1": [
    {
        "wins": "118",
        "losses": "40",
        "max_killed": "7",
        "battles": "158",
        "plane_id": "4401",
        "max_ground_object_destroyed": "3"
    },
    {
        "wins": "100",
        "losses": "58",
        "max_killed": "7",
        "battles": "158",
        "plane_id": "2401",
        "max_ground_object_destroyed": "3"
    },
    {
        "wins": "120",
        "losses": "38",
        "max_killed": "7",
        "battles": "158",
        "plane_id": "2403",
        "max_ground_object_destroyed": "3"
    }
],

"play2": [
    {
        "wins": "12",
        "losses": "450",
        "max_killed": "7",
        "battles": "158",
        "plane_id": "4401",
        "max_ground_object_destroyed": "3"
    },
    {
        "wins": "150",
        "losses": "8",
        "max_killed": "7",
        "battles": "158",
        "plane_id": "2401",
        "max_ground_object_destroyed": "3"
    },
    {
        "wins": "120",
        "losses": "328",
        "max_killed": "7",
        "battles": "158",
        "plane_id": "2403",
        "max_ground_object_destroyed": "3"
    }
],

Answer 1

fromJSON 返回一个列表，您可以使用*apply 函数遍历每个元素。 将其转换为“表格”（数据框是正确的 R 术语）相当简单（一旦您知道该怎么做！）。

library(rjson)

# You can pass directly the filename
my.JSON <- fromJSON(file="test.json")

df <- lapply(my.JSON, function(play) # Loop through each "play"
  {
  # Convert each group to a data frame.
  # This assumes you have 6 elements each time
  data.frame(matrix(unlist(play), ncol=6, byrow=T))
  })

# Now you have a list of data frames, connect them together in
# one single dataframe
df <- do.call(rbind, df)

# Make column names nicer, remove row names
colnames(df) <- names(my.JSON[[1]][[1]])
rownames(df) <- NULL

df
  wins losses max_killed battles plane_id max_ground_object_destroyed
1  118     40          7     158     4401                           3
2  100     58          7     158     2401                           3
3  120     38          7     158     2403                           3
4   12    450          7     158     4401                           3
5  150      8          7     158     2401                           3
6  120    328          7     158     2403                           3

Answer 2

我发现jsonlite 对这项任务更加用户友好。 Here is a comparison of three JSON parsing packages（偏向于jsonlite）

library(jsonlite)
data <- fromJSON('path/to/file.json')

data
#> $play1
#   wins losses max_killed battles plane_id max_ground_object_destroyed
# 1  118     40          7     158     4401                           3
# 2  100     58          7     158     2401                           3
# 3  120     38          7     158     2403                           3
# 
# $play2
#   wins losses max_killed battles plane_id max_ground_object_destroyed
# 1   12    450          7     158     4401                           3
# 2  150      8          7     158     2401                           3
# 3  120    328          7     158     2403                           3

如果您想将这些列表名称折叠到一个新列中，我推荐dplyr::bind_rows 而不是do.call(rbind, data)

library(dplyr)
data <- bind_rows(data, .id = 'play')

# Source: local data frame [6 x 7]

#    play  wins losses max_killed battles plane_id max_ground_object_destroyed
#   (chr) (chr)  (chr)      (chr)   (chr)    (chr)                       (chr)
# 1 play1   118     40          7     158     4401                           3
# 2 play1   100     58          7     158     2401                           3
# 3 play1   120     38          7     158     2403                           3
# 4 play2    12    450          7     158     4401                           3
# 5 play2   150      8          7     158     2401                           3
# 6 play2   120    328          7     158     2403                           3

请注意，列可能不是您期望的类型（请注意，列都是字符，因为所有数字都在提供的 JSON 数据中引用）！

2017 年 11 月编辑：类型转换的一种方法是使用 mutate_if 猜测字符列的预期类型。

data <- mutate_if(data, is.character, type.convert, as.is = TRUE)

Answer 3

我更喜欢 tidyjson 而不是 rjson 和 jsonlite，因为它具有将多级嵌套 json 对象转换为二维表的简单工作流程。使用来自 github 的这个包可以轻松解决您的问题。

devtools::install_github("sailthru/tidyjson")

library(tidyjson)
library(dplyr)

> json %>%  as.tbl_json %>% gather_keys %>% gather_array %>%  
+   spread_values(
+     wins = jstring("wins"),
+     losses = jstring("losses"),
+     max_killed = jstring("max_killed"),
+     battles = jstring("battles"),
+     plane_id = jstring("plane_id"),
+     max_ground_object_destroyed = jstring("max_ground_object_destroyed")
+    )

输出

  document.id   key array.index wins losses max_killed battles plane_id max_ground_object_destroyed
1           1 play1           1  118     40          7     158     4401                           3
2           1 play1           2  100     58          7     158     2401                           3
3           1 play1           3  120     38          7     158     2403                           3
4           1 play2           1   12    450          7     158     4401                           3
5           1 play2           2  150      8          7     158     2401                           3
6           1 play2           3  120    328          7     158     2403                           3