我有以下数据框，我想将其分成 10 个不同的数据框。我想将最初的 100 行数据框分成 10 行的 10 个数据框。我可以执行以下操作并获得所需的结果。
df = data.frame(one=c(rnorm(100)), two=c(rnorm(100)), three=c(rnorm(100)))
df1 = df[1:10,]
df2 = df[11:20,]
df3 = df[21:30,]
df4 = df[31:40,]
df5 = df[41:50,]
...
当然，当初始数据帧较大或无法轻松分解成多个段时，这不是执行此任务的优雅方式。
鉴于上述情况，假设我们有以下数据框。
df = data.frame(one=c(rnorm(1123)), two=c(rnorm(1123)), three=c(rnorm(1123)))
现在我想将其拆分为包含 200 行的新数据框，以及包含剩余行的最终数据框。执行此任务的更优雅（又名“快速”）方式是什么？
【问题讨论】：
> str(split(df, (as.numeric(rownames(df))-1) %/% 200))
List of 6
$ 0:'data.frame': 200 obs. of 3 variables:
..$ one : num [1:200] -1.592 1.664 -1.231 0.269 0.912 ...
..$ two : num [1:200] 0.639 -0.525 0.642 1.347 1.142 ...
..$ three: num [1:200] -0.45 -0.877 0.588 1.188 -1.977 ...
$ 1:'data.frame': 200 obs. of 3 variables:
..$ one : num [1:200] -0.0017 1.9534 0.0155 -0.7732 -1.1752 ...
..$ two : num [1:200] -0.422 0.869 0.45 -0.111 0.073 ...
..$ three: num [1:200] -0.2809 1.31908 0.26695 0.00594 -0.25583 ...
$ 2:'data.frame': 200 obs. of 3 variables:
..$ one : num [1:200] -1.578 0.433 0.277 1.297 0.838 ...
..$ two : num [1:200] 0.913 0.378 0.35 -0.241 0.783 ...
..$ three: num [1:200] -0.8402 -0.2708 -0.0124 -0.4537 0.4651 ...
$ 3:'data.frame': 200 obs. of 3 variables:
..$ one : num [1:200] 1.432 1.657 -0.72 -1.691 0.596 ...
..$ two : num [1:200] 0.243 -0.159 -2.163 -1.183 0.632 ...
..$ three: num [1:200] 0.359 0.476 1.485 0.39 -1.412 ...
$ 4:'data.frame': 200 obs. of 3 variables:
..$ one : num [1:200] -1.43 -0.345 -1.206 -0.925 -0.551 ...
..$ two : num [1:200] -1.343 1.322 0.208 0.444 -0.861 ...
..$ three: num [1:200] 0.00807 -0.20209 -0.56865 1.06983 -0.29673 ...
$ 5:'data.frame': 123 obs. of 3 variables:
..$ one : num [1:123] -1.269 1.555 -0.19 1.434 -0.889 ...
..$ two : num [1:123] 0.558 0.0445 -0.0639 -1.934 -0.8152 ...
..$ three: num [1:123] -0.0821 0.6745 0.6095 1.387 -0.382 ...
如果某些代码可能更改了行名，使用起来会更安全：
split(df, (seq(nrow(df))-1) %/% 200)
【讨论】：
require(ff)
df <- data.frame(one=c(rnorm(1123)), two=c(rnorm(1123)), three=c(rnorm(1123)))
for(i in chunk(from = 1, to = nrow(df), by = 200)){
print(df[min(i):max(i), ])
}
【讨论】：
如果你可以生成一个定义组的向量，你可以split任何东西：
f <- rep(seq_len(ceiling(1123 / 200)),each = 200,length.out = 1123)
> df1 <- split(df,f = f)
> lapply(df1,dim)
$`1`
[1] 200 3
$`2`
[1] 200 3
$`3`
[1] 200 3
$`4`
[1] 200 3
$`5`
[1] 200 3
$`6`
[1] 123 3
【讨论】：
像这样...？
b <- seq(10, 100, 10)
lapply(seq_along(b), function(i) df[(b-9)[i]:b[i], ])
[[1]]
one two three
1 -2.4157992 -0.6232517 1.0531358
2 0.6769020 0.3908089 -1.9543895
3 0.9804026 -2.5167334 0.7120919
4 -1.2200089 0.5108479 0.5599177
5 0.4448290 -1.2885275 -0.7665413
6 0.8431848 -0.9359947 0.1068137
7 -1.8168134 -0.2418887 1.1176077
8 1.4475904 -0.8010347 2.3716663
9 0.7264027 -0.3573623 -1.1956806
10 0.2736119 -1.5553148 0.2691115
[[2]]
one two three
11 -0.3273536 -1.92475496 -0.08031696
12 1.5558892 -1.20158371 0.09104958
13 1.9202047 -0.13418754 0.32571632
14 -0.0515136 -2.15669216 0.23099397
15 0.1909732 -0.30802742 -1.28651457
16 0.8545580 -0.18238266 1.57093844
17 0.4903039 0.02895376 -0.47678196
18 0.5125400 0.97052082 -0.70541908
19 -1.9324370 0.22093545 -0.34436105
20 -0.5763433 0.10442551 -2.05597985
[[3]]
one two three
21 0.7168771 -1.22902943 -0.18728871
22 1.2785641 0.14686576 -1.74738091
23 -1.1856173 0.43829361 0.41269975
24 0.0220843 1.57428924 -0.80163986
25 -1.0012255 0.05520813 0.50871603
26 -0.1842323 -1.61195239 0.04843504
27 0.2328831 -0.38432225 0.95650710
28 0.8821687 -1.32456215 -1.33367967
29 -0.8902177 0.86414661 -1.39629358
30 -0.6586293 -2.27325919 0.27367902
[[4]]
one two three
31 1.3810437 -1.0178835 0.07779591
32 0.6102753 0.3538498 1.92316801
33 -1.5034439 0.7926925 2.21706284
34 0.8251638 0.3992922 0.56781321
35 -1.0832114 0.9878058 -0.16820827
36 -0.4132375 -0.9214491 1.06681472
37 -0.6787631 1.3497766 2.18327887
38 -3.0082585 -1.3047024 -0.04913214
39 -0.3433300 1.1008951 -2.02065141
40 0.6009334 1.2334421 0.15623298
[[5]]
one two three
41 -1.8608051 -0.08589437 0.02370983
42 -0.1829953 0.91139017 -0.01356590
43 1.1146731 0.42384993 -0.68717391
44 1.9039900 -1.70218225 0.06100297
45 -0.4851939 1.38712015 -1.30613414
46 -0.4661664 0.23504099 -0.29335162
47 0.5807227 -0.87821946 -0.14816121
48 -2.0168910 -0.47657382 0.90503226
49 2.5056404 0.27574224 0.10326333
50 0.2238735 0.34441325 -0.17186115
[[6]]
one two three
51 1.51613140 -2.5630782 -0.6720399
52 0.03859537 -2.6688365 0.3395574
53 -0.08695292 -0.5114117 -0.1378789
54 -0.51878363 -0.5401962 0.3946324
55 -2.20482710 0.1716744 0.1786546
56 -0.28133749 -0.4497112 0.5936497
57 -2.38269088 -0.4625695 1.0048914
58 0.37865952 0.5055141 0.3337986
59 0.09329172 0.1560469 0.2835735
60 -1.10818863 -0.2618910 0.3650042
[[7]]
one two three
61 -1.2507208 -1.5050083 -0.63871084
62 0.1379394 0.7996674 -1.80196762
63 0.1582008 -0.3208973 0.40863693
64 -0.6224605 0.1416938 -0.47174711
65 1.1556149 -1.4083576 -1.12619693
66 -0.6956604 0.7994991 1.16073748
67 0.6576676 1.4391007 0.04134445
68 1.4610598 -1.0066840 -1.82981058
69 1.1951788 -0.4005535 1.57256648
70 -0.1994519 0.2711574 -1.04364396
[[8]]
one two three
71 1.23897065 0.4473611 -0.35452535
72 0.89015916 2.3747385 0.87840852
73 -1.17339703 0.7433220 0.40232381
74 -0.24568490 -0.4776862 1.24082294
75 -0.47187443 -0.3271824 0.38542703
76 -2.20899136 -1.1131712 -0.33663075
77 -0.05968035 -0.6023045 -0.23747388
78 1.19687199 -1.3390960 -1.37884241
79 -1.29310506 0.3554548 -0.05936756
80 -0.17470891 1.6198307 0.69170207
[[9]]
one two three
81 -1.06792315 0.04801998 0.08166394
82 0.84152560 -0.45793907 0.27867619
83 0.07619456 -1.21633682 -2.51290495
84 0.55895466 -1.01844178 -0.41887672
85 0.33825508 -1.15061381 0.66206732
86 -0.36041720 0.32808609 -1.83390913
87 -0.31595401 -0.87081019 0.45369366
88 0.92331087 1.22055348 -1.91048757
89 1.30491142 1.22582353 -1.32244004
90 -0.32906839 1.76467263 1.84479228
[[10]]
one two three
91 2.80656707 -0.9708417 0.25467304
92 0.35770119 -0.6132523 -1.11467041
93 0.09598908 -0.5710063 -0.96412216
94 -1.08728715 0.3019572 -0.04422049
95 0.14317455 0.1452287 -0.46133199
96 -1.00218917 -0.1360570 0.88864256
97 -0.25316855 0.6341925 -1.37571664
98 0.36375921 1.2244921 0.12718650
99 0.13345555 0.5330221 -0.29444683
100 2.28548261 -2.0413222 -0.53209956
【讨论】：
batchsize = 1000000 # vary to your liking
# cycles through data by batchsize
for (i in 1:ceiling(nrow(df)/batchsize))
{
print(i) # just to show the progress
# below shows how to cycle through data
batch <- df[(((i-1)*batchsize)+1(batchsize*i),,drop=FALSE] # drop = FALSE keeps it from being converted to a vector
# if below not done then the last batch has Nulls above the number of rows of actual data
batch <- batch[!is.na(batch$ID),] # ID is a variable I presume is in every row
#in this case the table already existed, if new table overwrite = TRUE
(dbWriteTable(con, "df", batch, append = TRUE,row.names = FALSE))
}
【讨论】：