Hi,
trees <- structure(list(Girth = c(8.3, 8.6, 8.8, 10.5, 10.7, 10.8, 11,
11, 11.1, 11.2, 11.3, 11.4, 11.4, 11.7, 12, 12.9, 12.9, 13.3,
13.7, 13.8, 14, 14.2, 14.5, 16, 16.3, 17.3, 17.5, 17.9, 18, 18,
20.6), Height = c(70L, 65L, 63L, 72L, 81L, 83L, 66L, 75L, 80L,
75L, 79L, 76L, 76L, 69L, 75L, 74L, 85L, 86L, 71L, 64L, 78L, 80L,
74L, 72L, 77L, 81L, 82L, 80L, 80L, 80L, 87L), Volume = c(10.3,
10.3, 10.2, 16.4, 18.8, 19.7, 15.6, 18.2, 22.6, 19.9, 24.2, 21,
21.4, 21.3, 19.1, 22.2, 33.8, 27.4, 25.7, 24.9, 34.5, 31.7, 36.3,
38.3, 42.6, 55.4, 55.7, 58.3, 51.5, 51, 77)), .Names = c("Girth",
"Height", "Volume"), row.names = c("1", "2", "3", "4", "5", "6",
"7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17",
"18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28",
"29", "30", "31"), class = "data.frame")
with(trees,cor(Volume,Height))
#[1] 0.5982497
with(trees,cor(Volume,Girth))
#[1] 0.9671194
trees$Volume[31]<- 35
with(trees,cor(Volume,Girth))
#[1] 0.9012941
with(trees,cor(Volume,Height))
[1] 0.5298093
#Looks like you ?attach() trees
attach(trees)
cor(Volume,Height)
#[1] 0.5298093
cor(Volume,Girth)
#[1] 0.9012941
trees[31,3] <- 77
You need to attach() again
attach(trees)
cor(Volume,Height)
#[1] 0.5982497
cor(Volume,Girth)
#[1] 0.9671194
It is better not to use ?attach(). Try using ?with()
A.K.
After having changed the last observation for Volume from 77.0 to 35,
> trees[31,3]<-35
> trees
Girth Height Volume
1 8.3 70 10.3
2 8.6 65 10.3
3 8.8 63 10.2
4 10.5 72 16.4
5 10.7 81 18.8
6 10.8 83 19.7
7 11.0 66 15.6
8 11.0 75 18.2
9 11.1 80 22.6
10 11.2 75 19.9
11 11.3 79 24.2
12 11.4 76 21.0
13 11.4 76 21.4
14 11.7 69 21.3
15 12.0 75 19.1
16 12.9 74 22.2
17 12.9 85 33.8
18 13.3 86 27.4
19 13.7 71 25.7
20 13.8 64 24.9
21 14.0 78 34.5
22 14.2 80 31.7
23 14.5 74 36.3
24 16.0 72 38.3
25 16.3 77 42.6
26 17.3 81 55.4
27 17.5 82 55.7
28 17.9 80 58.3
29 18.0 80 51.5
30 18.0 80 51.0
31 20.6 87 35.0
the correlation coefficient does not change, which it should...
earlier:
> cor(Volume, Girth)
[1] 0.9671194
> cor(Volume, Height)
[1] 0.5982497
and after changing value:
> cor(Volume, Girth)
[1] 0.9671194
> cor(Volume, Height)
[1] 0.5982497
Why is this?
Thanks in advance ;)
Victoria
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