将数据从像data.frame这样的列表转换为像data.frame这样的矩阵？答案

【问题标题】：Convert data from list like data.frame to matrix like data.frame?将数据从像data.frame这样的列表转换为像data.frame这样的矩阵？
【发布时间】：2017-10-21 09:42:32
【问题描述】：

我想将数据从列表形式转换为矩阵形式。

我的数据如下所示：

dataFrame.list

     compound    time    concentration
1    compA        1       0.5
2    compA        2       0.3
3    compB        2       0.7
4    compB        3       0.8
5    compA        3       0.5
6    compC        1       0.4
7    compC        3       0.1

我想以下列形式获得它：

     compound    time1     time2     time3
1    compA        0.5       0.3       0.5
2    compB        NA        0.7       0.8
3    compC        0.4       NA        0.1

我有几个问题：

dataframe.matrix

构造新的空数据框
使用变量名寻址正确的列。

这是我目前所拥有的：

# uniqe list of compounds
uniqueCompoundList <- unique(dataFrame.list$compound)


# unique vector of times
compoundTime <- as.character(sort(unique(dataFrame.list$time)))


# new matrix like dataframe (This doesn't work but kind of shows what I would like)
dataframe.matrix <- data.frame("compound", compoundTime)

for (singleCompound in uniqueCompoundList){

   # subset based on name
   singeCompoundData <- subset(dataFrame.list, compound == singleCompound)

   # put name in new matrix
   dataframe.matrix$compound <- compound

   for (time in singleCompound$time)){

     # put the value of concentration under the column equal to time
     dataframe.matrix$time <- singleCompound$concentration
   }

}

【问题讨论】：

标签： r dataframe

【解决方案1】：

我们可以使用dcast

library(reshape2)
dcast(df1, compound ~paste0("time", time))
#   compound time1 time2 time3
#1    compA   0.5   0.3   0.5
#2    compB    NA   0.7   0.8
#3    compC   0.4    NA   0.1

或与xtabs 来自base R

xtabs(concentration~compound + time, df1)

【讨论】：