How to replace a pair of observations in a matrix?

Dear all,

I did this replacement below and its work for the first case but not in the
second case! Please tell me what's wrong with the second case.....

Case 1:

m

[,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    3    6

l

[,1] [,2]
[1,]    9   10

matric1<-replace(m,m[3,],l)
matric1

[,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    9   10

matric2<-replace(m,m[3,],xy[50,])
matric2

[,1]      [,2]
[1,] 1.000000  4.000000
[2,] 2.000000  5.000000
[3,] 1.855060 -1.865495

(for matric2 xy[50,] is [1.855060, -1.865495]

Case 2:

xy<-cbind(x,y)
xy

x          y
 [1,] -1.2138881  1.0270690
 [2,]  0.5167578 -0.5793451
 [3,]  1.3342747 -1.2561305
 [4,]  0.3047976 -0.3411616
 [5,]  1.7300424 -1.9266858
 [6,]  1.6171193 -1.7818126
 [7,] -0.3296678  0.5010075
 [8,]  0.9840971 -0.8801955
 [9,] -0.5187400  0.4149603
[10,]  1.7179670 -1.6482844

m1<-replace(xy,xy[2,],l)
m1

x          y
 [1,] -1.2138881  1.0270690
 [2,]  0.5167578 -0.5793451
 [3,]  1.3342747 -1.2561305
 [4,]  0.3047976 -0.3411616
 [5,]  1.7300424 -1.9266858
 [6,]  1.6171193 -1.7818126
 [7,] -0.3296678  0.5010075
 [8,]  0.9840971 -0.8801955
 [9,] -0.5187400  0.4149603
[10,]  1.7179670 -1.6482844

l doesn't replace xy[2,]....(why??????)

Best regards

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