根据R中的值从矩阵返回列名 [英] Returning Column Name from Matrix based on value in R

问题描述

我有一个矩阵，希望根据该值提取列名.在这种情况下，我想要包含小于或等于2的值的任何列的名称(无论该值位于哪一行).

I have a matrix that I want to extract column names based on the value. In this case I want the name of any column that contains a value less than or equal to 2 (doesnt matter what row that value is located in).

set.seed(42)
DF <- matrix(sample(1:9,9),ncol=3,nrow=3)
DF <- as.data.frame.matrix(DF)

这是我尝试过的方法((如果矩阵中只有1行，这似乎可以奏效)

this is what I have tried, (it seems to work if there is only 1 row in the matrix)

test<-colnames(DF)[which(DF<=2),]

然后

test将表示包含值< = 2

test would then represent the column names containing values <= 2

推荐答案

1

在列上运行sapply并找到min，然后检查min是否满足您的条件.

1

Run sapply over columns and find min and then check if the min meets your condition.

colnames(DF)[sapply(DF, min) <= 2]
#[1] "V3"

2

您还可以在列(MARGIN = 2)上运行apply，以查看每列中的any值是否满足要求的条件

2

You can also run apply on columns (MARGIN = 2) to see if any value in each column meets the required condition

colnames(DF)[apply(DF, MARGIN = 2, function(a) any(a<=2))]
#[1] "V3"

3

将arr.ind = TRUE与which一起使用.这将给出满足which条件的值的索引.从中提取列信息[,2].

3

Use arr.ind = TRUE with which. This will give the indices of the values that meet the condition of which. From that, extract the column information [,2].

unique(colnames(DF)[which(DF<=2, arr.ind = TRUE)[,2]])
#[1] "V3"

数据

set.seed(42)
DF <- matrix(sample(1:9,9),ncol=3,nrow=3)
DF <- as.data.frame.matrix(DF)
DF
#  V1 V2 V3
#1  9  5  6
#2  8  4  1
#3  3  7  2

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