Dear Friends,
   I want to extract the records from A according to B, but the results are
not correct because R says :
  The length of long object is not integer times on the length of short
object.
  Anybody have met the same problem? How to do it correctly?

length(A)=47
length(B)=6

A[A$coords.x1==B$X1,]   #the program for the above task. I should get 6
records, but i only get former 4 records for the above reason.

Thanks.
 The folloing shows dataset A and B.


> A
   coords.x1 coords.x2
0  542250.89 3392404.1
1  538813.87 3388339.0
2  536049.19 3385821.6
3  533659.62 3383194.2
4  530642.30 3376834.9
5  529573.15 3378177.8
6  530853.82 3394838.8
7  541512.51 3394721.6
8  541479.33 3394877.8
9  538903.39 3395942.5
10 536019.95 3396286.1
11 538675.23 3384213.2
12 535127.95 3381255.4
13 533852.24 3378660.4
14 531360.91 3379273.8
15 539289.14 3375759.8
16 543410.51 3384353.1
17 543089.27 3388170.1
18 543274.03 3389919.2
19 543840.77 3392012.4
20 553383.55 3402401.8
21 554621.51 3397938.9
22 564096.42 3397524.4
23 567529.64 3398702.9
24 561798.76 3404864.0
25 562868.34 3405502.2
26 563145.22 3403192.1
27 562419.87 3404090.4
28 558321.85 3403879.9
29 567050.74 3404973.1
30 570609.70 3408742.4
31 556777.57 3397858.0
32 531353.38 3368596.6
33 533513.50 3372749.3
34 537543.19 3364284.8
35 538779.41 3368224.8
36 525930.09 3374067.7
37 522990.85 3369213.1
38 528826.37 3359019.0
39 533865.85 3362595.4
40 531200.25 3365053.0
41 551054.10 3377181.3
42 546974.19 3369284.8
43 572315.59 3359541.1
44 562703.63 3355173.4
45 558959.31 3357804.4
46 558531.39 3361741.1


> B
         X1        X2
1 542250.89 3392404.1
2 541512.51 3394721.6
3 541479.33 3394877.8
4 538903.39 3395942.5
5 543274.03 3389919.2
6 543840.77 3392012.4

-- 
With Kind Regards,

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Zhi Jie,Zhang ,PHD
Tel:86-21-54237149
Dept. of Epidemiology,School of Public Health,Fudan University
Address:No. 138 Yi Xue Yuan Road,Shanghai,China
Postcode:200032
Email:epistat@gmail.com
Website: www.statABC.com
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