如何将 MATLAB 结构加载到 R 数据框中? [英] How to load a MATLAB struct into a R data frame?

问题描述

我有一个 MATLAB 结构体，其中包含多个字段，这些字段共同描述了多个变量的 100 个观察值，如下(MATLAB 输出):

I have a MATLAB struct, containing a number of fields which together describe, say, 100 observations of a number of variables, as follows (MATLAB output):

mystruct = 

  fieldA: [100x1 double]
  fieldB: [100x1 double]
  fieldC: [100x1 double]
  fieldD: [100x1 char]
  fieldE: {100x1 cell}

我想对这些数据使用 R，所以我将结构保存为 .mat 文件.并使用 R.matlab 包导入它.因为我是 R 的新手，以下内容可能很笨拙，但我可以很好地访问各个字段(R 代码):

I want to use R with this data, so I save the struct as a .mat file. and import it using the R.matlab package. Because I'm new to R, the following is likely clumsy, but I can access individual fields just fine (R code):

> f = readMat('myfile.mat')
> data = f$mystruct
> data
  , , 1

      [,1]         
  fieldA Numeric,100  
  fieldB Numeric,100  
  fieldC Numeric,100  
  fieldD Character,100
  fieldE List,100   

> data = data[, , 1]
> df <- data.frame(fieldA = data$fieldA, fieldB = data$fieldB)

好的，那么问题来了:如何概括上述内容，以便为原始结构中的任意数量的字段生成数据框?对于我的 5-field 示例，我可以手动完成，但是我的下一个数据集有很多字段，我不想全部输入.

OK, so here is the question: how can I generalize the above so that a data frame is generated for an arbitrary number of fields in the original struct? For my 5-field example I can manually do it, but the next data set I have has many fields, and I don't want to enter them all.

根据这个问题，我尝试了rbind() 和 ldply()，它们构建了超大尺寸的数据框(分别为 1 个变量的 401 个 obs 和 105 个变量的 401 个 obs).

As per this question, I tried rbind() and ldply(), which construct outrageously dimensioned data frames (401 obs of 1 variable and 401 obs of 105 variables respectively).

推荐答案

事实证明，MATLAB 元胞数组 (fieldE) 是作为嵌套列表导入的.使用 unlist 可以解决这个问题:

As it turns out, the MATLAB cell array (fieldE) was imported as a nested list. Using unlist takes care of the problem:

data = lapply(data, unlist, use.names=FALSE)
df <- as.data.frame(data) # now has correct number of obs and vars

感谢@koekenbakker 提供对此的关键指针！

Thanks @koekenbakker for the critical pointer to this!

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