Indexing/Slicing/Subsetting

General
#1

Hello everyone,

I am still a beginner so sorry for that very basic question :slight_smile:
I am wondering why I am getting that error message in the second code line, while slicing x with c(TRUE, FALSE) works out.
I thought that, ,if one vector is shorter than the other, R will repeat the shorter vector. So I would expect x[TRUE, FALSE] to produce the same result as x[c(TRUE, FALSE)] does?

Thanks for your help!

x<-3:10

x[c(TRUE, FALSE)]
[1] 3 5 7 9

x[TRUE, FALSE]
error in x[TRUE, FALSE] :wrong number of dimensions

#2

In the first code, you provide a single indexing vector of length 2, namely c(TRUE, FALSE). Yes, this vector will be recycled until all the elements of x are covered.

In the second code, you do not have single indexing vector. Rather, you have provided a row indexing vector, namely c(TRUE), and a column indexing vector, namely c(FALSE). R is confused and is wondering why you are supplying row and column indexes for a 1 dimensional object, i.e., the vector x.

You may wish to go through the swirl package for a tutorial on vectors.

install.packages("swirl")
library("swirl")
swirl()

Hope that helps,
Snehal

2 Likes
#3

Yes, that helps, thank you!!

And I didn't know swirl yet, but it looks very good! The swirl() command does not seem to work - should it present me with course options? Or do I need to install courses from github first?

#4

You can use the three lines of code in my initial response to install the package, load the library, and then launch the program.

#5

Hmm, I can install the package and read the help function. But when I put in swirl() R says it can't find the function swirl. But Ill guess Ill find my way through it tomorrow:) Thank you very much for your advice!

#6

Did you load the package as well with library("swirl")?

#7

Yes, I did.. I get an error message saying that the package "RCurl" is not installed. I tried to install that but R says there is no package called "RCurl". I tried installing "curl" as I randomly saw it in my user library. But that didnt help either. Anyway, I can access the help function of the swirl-package and I simply need to find a way to start one of the courses :slight_smile:

#8

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