直接从JSON文件获取数据帧? [英] Getting dataframe directly from JSON-file?

问题描述

首先，让我感谢所有为Stackoverflow和R做出贡献的人！我是那些不太擅长编程的R用户之一，但是勇敢地尝试将其用于工作，因此下面的问题可能很简单...

First, let me thank everybody who contributes to Stackoverflow and R! I'm one of those R-users who is not so good at programming, but bravely try to use it for work, so the issue below is probably trivial...

这是问题所在.我需要将JSON格式的文件导入R:

Here's the problem. I need to import files in JSON-format to R:

# library(plyr)
# library(RJSONIO)
# lstJson <- fromJSON("JSON_test.json")        #This is the file I read
# dput(lstJson)                                              #What I did to get the txtJson below, for the benefit of testing.

txtJson <- structure(list(version = "1.1", result = structure(list(warnings = structure(list(), class = "AsIs"), fields = list(structure(list(info = "", rpl = 15, name = "time", type = "timeperiod"), .Names = c("info", "rpl", "name", "type")), structure(list(info = "", name = "object", type = "string"), .Names = c("info", "name", "type")), structure(list(info = "Counter1", name = "Counter1", type = "int"), .Names = c("info", "name", "type")), structure(list( info = "Counter2", name = "Counter2", type = "int"), .Names = c("info", "name", "type"))), timeout = 180, name = NULL, data = list( list(list("2011-05-01 17:00", NULL), list("Total", NULL), list(8051, NULL), list(44, NULL)), list(list("2011-05-01 17:15", NULL), list("Total", NULL), list(8362, NULL), list( 66, NULL))), type = "AbcDataSet"), .Names = c("warnings", "fields", "timeout", "name", "data", "type"))), .Names = c("version", "result"))

dfJson <- ldply(txtJson, data.frame)  

我需要的是与此相似的数据框:

What I need is a data frame similar to this:

time  object  Counter1  Counter2  
2011-05-01 17:00  Total  8051  44  
2011-05-01 17:15  Total  8362  66 

但是我得到了

"Error in data.frame("2011-05-01 17:00", NULL, check.names = FALSE, stringsAsFactors = TRUE) : 
  arguments imply differing number of rows: 1, 0"

如果我使用lstJson，也会遇到相同的错误.

I get the same error if I use the lstJson.

我不确定RJSONIO是否应该足够聪明"来解析此类文件，或者我是否必须手动读取文件的第一行，设置列类型等.原因是我不使用CSV的原因是我想自动"获取日期格式等的日期.

I'm not sure if RJSONIO is supposed to be "smart enough" to parse files like this, or if I have to manually read the first line of the file, set column-types etc. The reason I'm not using CSV is that I want to "automatically" get dates in date-format, etc.

谢谢， /克里斯

推荐答案

查看txtJson的结构，您会发现所有有用的位都在txtJson $ result $ data中:

Looking at the structure of txtJson you see that all of the useful bits are in txtJson$result$data:

> sapply( txtJson$result$data, unlist )
     [,1]               [,2]              
[1,] "2011-05-01 17:00" "2011-05-01 17:15"
[2,] "Total"            "Total"           
[3,] "8051"             "8362"            
[4,] "44"               "66"              
> t(sapply( txtJson$result$data, unlist ))
     [,1]               [,2]    [,3]   [,4]
[1,] "2011-05-01 17:00" "Total" "8051" "44"
[2,] "2011-05-01 17:15" "Total" "8362" "66"
> as.data.frame(t(sapply( txtJson$result$data, unlist )) )
                V1    V2   V3 V4
1 2011-05-01 17:00 Total 8051 44
2 2011-05-01 17:15 Total 8362 66

在将它们作为未列出的向量进行获取然后传递给"as.data.frame"的过程中，它们现在都是因子"类，因此可能需要付出更多的努力来重新分类()这些值.您可以改用:

In the process of gettting these as unlisted vectors and then passing to 'as.data.frame' they are now all class 'factor', so there is probably additional effort to re-class() these values. You can instead use:

data.frame(t(sapply( txtJson$result$data, unlist )) ,stringsAsFactors=FALSE)

它们都是字符"

对于导入CSV文件，read.table()的colClasses参数将接受"POSIXlt"或"POSIXct"作为已知类型.我相信规则是必须有一个as. _ 方法可用.这是一个最小的示例:

As far as importing CSV files, read.table()'s colClasses argument will accept "POSIXlt" or "POSIXct" as known types. The rule I believe is that there must an as._ method available. Here's a minimal example:

> read.table(textConnection("2011-05-01 17:00"), sep=",", colClasses="POSIXct")
                   V1
1 2011-05-01 17:00:00

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