如何索引R中列表对象的元素 [英] How to index an element of a list object in R

问题描述

我正在执行以下操作以导入一些txt表并将它们保存为列表：

I'm doing the following in order to import some txt tables and keep them as list:

# set working directory - the folder where all selection tables are stored
hypo_selections<-list.files() # change object name according to each species
hypo_list<-lapply(hypo_selections,read.table,sep="\t",header=T) # change object name according to each species

我想访问一个特定元素，让我们说hypo_list [1]。由于每个元素代表一个表，我应该如何获取访问特定单元格（行和列）？

I want to access one specific element, let's say hypo_list[1]. Since each element represents a table, how should I procced to access particular cells (rows and columns)?

我想做类似的事情：

a<-hypo_list[1]

a[1,2]

但我收到以下错误消息：

But I get the following error message:

Error in a[1, 2] : incorrect number of dimensions

是否有一种聪明的方法可以做到这一点？

Is there a clever way to do it?

提前致谢！

推荐答案

索引列表已完成使用双括号，即 hypo_list [[1]] （例如，看看这里： http://www.r-tutor.com/r-introduction/list ）。 BTW： read.table 不返回表而是返回数据帧（请参阅中的值部分？read.table ）。因此，您将拥有一个数据框列表，而不是一个表对象列表。表格和数据框架的主要机制相同。

Indexing a list is done using double bracket, i.e. hypo_list[[1]] (e.g. have a look here: http://www.r-tutor.com/r-introduction/list). BTW: read.table does not return a table but a dataframe (see value section in ?read.table). So you will have a list of dataframes, rather than a list of table objects. The principal mechanism is identical for tables and dataframes though.

注意：在R中，第一个条目的索引是 1 （不是 0 与其他一些语言一样）。

Note: In R, the index for the first entry is a 1 (not 0 like in some other languages).

数据帧

l <- list(anscombe, iris)   # put dfs in list
l[[1]]             # returns anscombe dataframe

anscombe[1:2, 2]   # access first two rows and second column of dataset
[1] 10  8

l[[1]][1:2, 2]     # the same but selecting the dataframe from the list first
[1] 10  8

表格对象

tbl1 <- table(sample(1:5, 50, rep=T))
tbl2 <- table(sample(1:5, 50, rep=T))
l <- list(tbl1, tbl2)  # put tables in a list

tbl1[1:2]              # access first two elements of table 1 

现在有了清单

l[[1]]                 # access first table from the list

1  2  3  4  5 
9 11 12  9  9 

l[[1]][1:2]            # access first two elements in first table

1  2 
9 11 

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