CODEWITHSUNDEEP
r
Samoth
Samoth

Reputation: 756

Another way to indicate variable from a given data frame?

My question seems to be easy but difficult to describe, see the code below. Let's create a data frame first:

Length<-c(10,11,9,8,10)
Width<-c(5,5.4,4.7,5.6,6.1)
Layer<-c(8,10,12,10,14) 
data<-data.frame(Length, Width, Layer)
data
    Length Width Layer
1     10   5.0     8
2     11   5.4    10
3      9   4.7    12
4      8   5.6    10
5     10   6.1    14

And as we all know, if we'd like to indicate variable from a given data frame, we need to type as below:

data$Layer
[1]  8 10 12 10 14

However, when there are many variables it becomes time consuming so I'd like to find other ways:

var_list<-c("Length", "Width", "Layer")
var_list
[1] "Length" "Width"  "Layer" 
> var_list[1]
[1] "Length"
> var_list[2]
[1] "Width"
> var_list[3]
[1] "Layer"

So a variable list is created, and I'd like to use this to indicate to the data set but in vain:

> data$var_list
  NULL
> data$var_list[1]
  NULL
> data$var_list[2]
  NULL
> data$var_list[3]
  NULL

Hope my description is clear enough and thanks in advance for any ideas or suggestions.

Upvotes: 1

Views: 70

Answers (1)

bgoldst
bgoldst

Reputation: 35324

1: you can get the names of the columns via the names() function:

names(data);
## [1] "Length" "Width"  "Layer"

2: You can extract a single column using the `[[`() operation:

data[['Layer']];
## [1]  8 10 12 10 14
data[[names(data)[3L]]];
## [1]  8 10 12 10 14

3: But since you end up using a numeric index into the vector of names anyway, I suggest you simply use numeric indexing on the original data.frame:

data[[3L]];
## [1]  8 10 12 10 14

Upvotes: 2

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