如何迭代R中的数据帧列表

I have a list in R that contains several data frames. I want to iterate over the data frames and calculate the min/max of a value from the data frame. Here's the code that I have right now:

我在R中有一个包含几个数据框的列表。我想迭代数据帧并计算数据帧中值的最小值/最大值。这是我现在的代码：

firstname = names(dats)[1]
xlim = c( min( dats[[firstname]][,xlab] ), max( dats[[firstname]][,xlab] ) )
for ( name in names(dats) ) {
   xlim = c( min(xlim[1],dats[[name]][,xlab]), max(xlim[2],dats[[name]][,xlab]) )
}

This seems ugly to me, as it requires a lot of code to do something very simple. Is there a more canonical way to do this in R?

这对我来说似乎很难看，因为它需要很多代码来做一些非常简单的事情。在R中有更典型的方法吗？

3 个解决方案

#1

You can use lapply to extract the xlab column out of all the data-frames, and unlist to combine into one vector, then take the min or max:

您可以使用lapply从所有数据帧中提取xlab列，并取消列表以组合成一个向量，然后取最小值或最大值：

xlab <- 'a'
dats <- list( df1 = data.frame(a=sample(1:3), b = sample(11:13)),
              df2 = data.frame(a=sample(1:3), b = sample(11:13)))

>  min( unlist( lapply( dats, '[', xlab ) ) )
[1] 1
>  max( unlist( lapply( dats, '[', xlab ) ) )
[1] 3

#2

Can you combine the data frames from the list of data frames into one data frame? I would use the plyr package and rbind.fill, which would allow the data frames to have mismatched columns as long as the column of interest is named the same in all data frames.

您能否将数据帧列表中的数据帧合并为一个数据帧？我会使用plyr包和rbind.fill，这将允许数据帧具有不匹配的列，只要感兴趣的列在所有数据帧中被命名为相同。

library(plyr)
df.orig <- data.frame(one = rep(1:4, each = 4), two = 1:16)
df.list <- dlply(df.orig, "one")
df.new <- rbind.fill(df.list)
xlim <- with(df.new, c(min(two), max(two)))

#3

If I understand the question correctly, heres something to do with plyr:

如果我正确地理解了这个问题，那就是与plyr有关：

dats <- list( df1 = data.frame(a=sample(1:3), b = sample(11:13)),
              df2 = data.frame(a=sample(1:3), b = sample(11:13)))

library(plyr)

xlim <- adply(do.call("rbind",dats),2,function(x)c(min(x),max(x)))
    names(xlim)=c("xlab","min","max")

xlim
  xlab min max
1    a   1   3
2    b  11  13

Gives per variable the minimum and maximum collapsed over all data frames in the list.

为每个变量提供列表中所有数据框的最小和最大折叠。

EDIT: shortened the code abit. I do assume that each dataframe contains the same number of columns in the same order.

编辑：缩短代码abit。我假设每个数据帧包含相同顺序的相同列数。

#1