[R] Masking

[David Arnold]

Hi,

I'm a bit confused by masking. Thought I understood, but today makes me
wonder.

x=0:9
y=0:9
sm=data.frame(x=4:8,y=9:13)
attach(sm)
x
detach(sm)

The code produces this message:

> attach(sm)
The following object is masked _by_ .GlobalEnv:

    x, y

> x
 [1] 0 1 2 3 4 5 6 7 8 9

I guess I thought that when you attach a dataframe, then the values in the
dataframe now override any existing variables in your workspace with the
same name. But this example seems to say that if I have something in my data
frame with the same name as an existing variable in my workspace, if I
attach the data frame, then it won't be the variable in the data frame that
is in play, but the existing variable in my workspace.

Have I learned my lesson?

And what are those commands that help you see what will be searched first,
second, third ... for a variable in your code?

D.



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