# What does this R command translate into in plain English?

#### user366312

Gold Member
Summary
mean(mat[2, mat[1, ] == 1] == 1)

What does this R command translate into plain English?
According to my understanding:

So the mean is: (1+1+2+1)/4 = 1.25.

Is my understanding correct?

If I am correct, what does it actually try to achieve?

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#### Ygggdrasil

Gold Member
mean(mat[2, mat[1, ] == 1] == 1)
Why would anyone write a command like that?

It helps to break the problem down into steps:
• First, consider what does mat[1,] evaluate as?
• Next, what is the output of mat[1,]==1?
• Next, what is mat[2, mat[1, ] == 1]?
• Next, what is mat[2, mat[1, ] == 1] == 1?
• Finally, you can calculate mean(mat[2, mat[1, ] == 1] == 1).
Given the matrix you provide in the OP, I get 0.5 as the final answer.

#### user366312

Gold Member
Given the matrix you provide in the OP, I get 0.5 as the final answer.
Yeah, I figured that out myself.

Thanks for the help anyway.

#### sysprog

Yeah, I figured that out myself.

Thanks for the help anyway.
That response looks as if you cared mainly about the answer, and not so much about the specifics of the clarifyingly cogent method carefully elucidated by @Ygggdrasil by which he arrived at it.

I'm sure your gratitude is appreciated by him; however, your edification would be immensely more gratifying.

Please at least don't fail to notice the value of the innermost-first innermore-next approach taken to parsing the expression.

#### user366312

Gold Member
That response looks as if you cared mainly about the answer, and not so much about the specifics of the clarifyingly cogent method carefully elucidated by @Ygggdrasil by which he arrived at it.

I'm sure your gratitude is appreciated by him; however, your edification would be immensely more gratifying.

Please at least don't fail to notice the value of the innermost-first innermore-next approach taken to parsing the expression.

I spent almost 4 hours on this to understand it properly.

#### sysprog

user366312 said:

I spent almost 4 hours on this to understand it properly.
I didn't mean to disparage the value of your thinking things through for yourself. When I posted, I of course could not see all the avenues of your reasoning, and was responding merely as an observer of the prior posts. Thanks for reading and responding to what I wrote.

"What does this R command translate into in plain English?"

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