> v <- rnorm(100)
> v
[1] 0.27490871 -0.57161078 0.64020986 -0.39754722 1.32424165 0.06347008
[7] 0.20677276 -0.66588559 0.61941635 -0.13207990 0.42546491 -0.92988025
[13] 0.43543220 -0.23062783 0.16941551 -0.17475767 0.62665430 0.68266342
[19] 0.45717638 -0.30739560 0.72572294 -1.77361180 0.45883414 -1.98110452
[25] -0.29350379 -0.82418397 -0.81337914 -0.93465004 0.43031325 -0.55386505
[31] -0.26281165 0.70885023 0.12152812 0.33321883 -0.43545927 1.37405349
[37] -1.71264136 -0.27165682 -0.36502102 0.31350061 0.03345427 -0.71804601
[43] 1.24106912 -0.57789687 0.45415339 0.12761564 -1.27978008 -2.47963828
[49] 0.67876950 0.50651155 1.04199976 -0.14985713 -0.41280677 -0.33707072
[55] -1.89268042 1.10675489 0.44384364 0.87062916 -0.59833929 -1.27289285
[61] -0.10245473 0.79828687 -1.14070205 1.75745412 -1.78495571 0.40220049
[67] -0.07877791 -1.63648385 0.95018039 -1.19699479 -0.01775036 -1.68831766
[73] -0.75387562 0.91782210 0.02007090 -0.21014391 -0.56826407 -0.46589752
[79] -1.24972758 0.06181393 0.11990013 0.51829362 0.42814208 -1.76231873
[85] 0.44012318 -0.83641060 -1.22257877 -0.79810554 0.89512719 0.74075451
[91] 0.30737719 -0.36606714 1.22049269 0.44840424 -1.44563892 0.37973309
[97] -1.08454584 -0.03219926 0.65801561 -0.26380084
> v[10]
[1] -0.1320799
> v[10:20]
[1] -0.1320799 0.4254649 -0.9298802 0.4354322 -0.2306278 0.1694155
[7] -0.1747577 0.6266543 0.6826634 0.4571764 -0.3073956
> v[20:30]
[1] -0.3073956 0.7257229 -1.7736118 0.4588341 -1.9811045 -0.2935038
[7] -0.8241840 -0.8133791 -0.9346500 0.4303132 -0.5538650
> v[v>0]
[1] 0.27490871 0.64020986 1.32424165 0.06347008 0.20677276 0.61941635
[7] 0.42546491 0.43543220 0.16941551 0.62665430 0.68266342 0.45717638
[13] 0.72572294 0.45883414 0.43031325 0.70885023 0.12152812 0.33321883
[19] 1.37405349 0.31350061 0.03345427 1.24106912 0.45415339 0.12761564
[25] 0.67876950 0.50651155 1.04199976 1.10675489 0.44384364 0.87062916
[31] 0.79828687 1.75745412 0.40220049 0.95018039 0.91782210 0.02007090
[37] 0.06181393 0.11990013 0.51829362 0.42814208 0.44012318 0.89512719
[43] 0.74075451 0.30737719 1.22049269 0.44840424 0.37973309 0.65801561
> y <- data.frame(a=rnorm(100), b=1:100, cc=sample(letters, 100, replace=TRUE))
> y
a b cc
1 -1.05072407 1 z
2 -0.18633727 2 s
3 1.51275200 3 c
4 0.38983023 4 k
5 -2.14125663 5 d
6 1.09490895 6 v
7 -0.89677117 7 o
8 0.70987843 8 j
9 0.36386986 9 w
10 0.44675961 10 h
11 0.33963430 11 p
12 1.73164715 12 h
13 -0.69733418 13 a
14 -1.53740599 14 i
15 1.08173190 15 z
16 0.05837664 16 k
17 -0.18728485 17 s
18 -2.24779692 18 d
19 -0.22513533 19 b
20 0.81450061 20 t
21 -0.17749919 21 k
22 -1.41690777 22 r
23 -0.72529640 23 r
24 0.82405243 24 l
25 0.53325251 25 b
26 0.46904192 26 e
27 -0.08400868 27 l
28 2.21477565 28 u
29 0.27947719 29 q
30 -0.77089822 30 r
31 -1.47788058 31 l
32 0.82794892 32 f
33 0.27566156 33 g
34 1.38891677 34 z
35 -0.30216594 35 r
36 0.59136053 36 p
37 0.81394706 37 f
38 -1.26644041 38 s
39 1.66906478 39 z
40 -1.30537544 40 u
41 -0.61211346 41 p
42 -0.74495805 42 h
43 0.93707928 43 v
44 -0.06270301 44 y
45 0.13184642 45 z
46 1.68170317 46 t
47 0.65853512 47 o
48 0.29435463 48 c
49 -0.77810967 49 j
50 2.44036151 50 j
51 -0.61516533 51 h
52 -0.18756104 52 o
53 -0.66418894 53 m
54 0.42557636 54 j
55 -0.10565081 55 r
56 0.25471350 56 x
57 0.13600198 57 o
58 -1.34409656 58 p
59 -1.21763325 59 y
60 1.18913484 60 b
61 0.95020395 61 v
62 1.26743614 62 h
63 1.93673889 63 r
64 -0.20036786 64 f
65 1.40333198 65 s
66 -1.26916665 66 p
67 0.43765404 67 x
68 1.29766523 68 t
69 -0.16819836 69 v
70 0.66117636 70 n
71 0.19013903 71 s
72 0.57311887 72 d
73 -0.70807418 73 u
74 0.55397272 74 r
75 -0.45071446 75 v
76 0.16809683 76 a
77 0.36223258 77 l
78 1.32103523 78 z
79 1.96134005 79 j
80 0.38271909 80 s
81 1.27897625 81 g
82 1.78663875 82 i
83 1.31121478 83 f
84 -0.61360892 84 l
85 -0.04370639 85 c
86 -1.79322292 86 x
87 1.59709341 87 t
88 -0.11716048 88 h
89 0.16692663 89 s
90 0.91605049 90 t
91 -0.61338218 91 x
92 -0.56781001 92 x
93 0.56461762 93 u
94 -0.38071338 94 l
95 1.40079416 95 i
96 -1.32747355 96 a
97 0.01799297 97 a
98 0.32938497 98 z
99 -0.59506751 99 e
100 -0.61649221 100 p
> tail(y, 10)
a b cc
91 -0.61338218 91 x
92 -0.56781001 92 x
93 0.56461762 93 u
94 -0.38071338 94 l
95 1.40079416 95 i
96 -1.32747355 96 a
97 0.01799297 97 a
98 0.32938497 98 z
99 -0.59506751 99 e
100 -0.61649221 100 p
> y[10:20,]
a b cc
10 0.44675961 10 h
11 0.33963430 11 p
12 1.73164715 12 h
13 -0.69733418 13 a
14 -1.53740599 14 i
15 1.08173190 15 z
16 0.05837664 16 k
17 -0.18728485 17 s
18 -2.24779692 18 d
19 -0.22513533 19 b
20 0.81450061 20 t
> y[10,"b"]
[1] 10
> y["cc"]
cc
1 z
2 s
3 c
4 k
5 d
6 v
7 o
8 j
9 w
10 h
11 p
12 h
13 a
14 i
15 z
16 k
17 s
18 d
19 b
20 t
21 k
22 r
23 r
24 l
25 b
26 e
27 l
28 u
29 q
30 r
31 l
32 f
33 g
34 z
35 r
36 p
37 f
38 s
39 z
40 u
41 p
42 h
43 v
44 y
45 z
46 t
47 o
48 c
49 j
50 j
51 h
52 o
53 m
54 j
55 r
56 x
57 o
58 p
59 y
60 b
61 v
62 h
63 r
64 f
65 s
66 p
67 x
68 t
69 v
70 n
71 s
72 d
73 u
74 r
75 v
76 a
77 l
78 z
79 j
80 s
81 g
82 i
83 f
84 l
85 c
86 x
87 t
88 h
89 s
90 t
91 x
92 x
93 u
94 l
95 i
96 a
97 a
98 z
99 e
100 p
> z <- c(1, 2, 3, NA, 4, NA, 5, NA)
> z[!is.na(z)]
[1] 1 2 3 4 5
> mean(z, trim=0, na.rm=TRUE)
[1] 3
> mean(z, trim=0, na.rm=FALSE)
[1] NA