lapply để run functions lặp lại cho một nhóm các đối tượng
x <- list(a = 1:4, b = rnorm(10), c = rnorm(20, 1), d = rnorm(100, 5))
x## $a
## [1] 1 2 3 4
##
## $b
## [1] 0.44899476 -0.34083084 0.34853326 1.14808473 -0.07618802 -0.29947369
## [7] 0.40756918 -1.08342935 0.28415112 0.79421043
##
## $c
## [1] 0.1831717513 -1.3764995555 1.0328178379 0.6498577211 2.5776086438
## [6] 1.9290229365 1.2279577308 0.3422590467 0.1465789761 0.6548412349
## [11] 1.9241546366 1.7236659692 0.0004261627 1.8049186650 0.0489684161
## [16] 1.4140868694 2.3744689834 1.0589785459 1.3150997296 0.9783728059
##
## $d
## [1] 4.693842 6.118469 4.963846 4.039952 5.428887 3.196418 5.615257 3.896050
## [9] 5.271312 4.546851 5.841589 4.919419 4.597131 4.447585 4.795010 5.158126
## [17] 5.204699 4.302329 5.920463 4.604543 4.424102 5.324469 4.693661 4.968281
## [25] 3.702152 6.247600 4.374264 4.760129 5.841408 6.229371 4.202510 5.727730
## [33] 5.489549 5.636130 5.718669 4.022112 2.794614 5.314578 5.122858 4.745450
## [41] 6.911959 5.705176 4.319500 5.580554 4.925161 5.882415 5.041602 6.230771
## [49] 5.073165 4.899730 6.079619 5.145594 4.728582 2.144772 4.266203 5.134112
## [57] 5.108570 3.756038 4.550302 3.587848 6.036117 2.791455 6.397301 6.839394
## [65] 4.915022 5.622709 5.015916 4.441438 3.300368 5.726474 5.858424 5.889120
## [73] 4.479478 6.140046 5.005719 5.471583 6.063969 4.239001 5.227279 5.976799
## [81] 4.944041 3.973517 4.615122 4.623892 6.953635 5.970248 4.889914 5.050718
## [89] 4.106434 5.254330 6.839574 2.279943 4.690487 5.528427 4.365232 5.007320
## [97] 4.618103 5.675009 5.973018 6.234608lapply(x, mean)## $a
## [1] 2.5
##
## $b
## [1] 0.1631622
##
## $c
## [1] 1.000538
##
## $d
## [1] 5.030043library(datasets)
head(airquality)## Ozone Solar.R Wind Temp Month Day
## 1 41 190 7.4 67 5 1
## 2 36 118 8.0 72 5 2
## 3 12 149 12.6 74 5 3
## 4 18 313 11.5 62 5 4
## 5 NA NA 14.3 56 5 5
## 6 28 NA 14.9 66 5 6Spliting data frame by groups
## List of 5
## $ 5:'data.frame': 31 obs. of 6 variables:
## ..$ Ozone : int [1:31] 41 36 12 18 NA 28 23 19 8 NA ...
## ..$ Solar.R: int [1:31] 190 118 149 313 NA NA 299 99 19 194 ...
## ..$ Wind : num [1:31] 7.4 8 12.6 11.5 14.3 14.9 8.6 13.8 20.1 8.6 ...
## ..$ Temp : int [1:31] 67 72 74 62 56 66 65 59 61 69 ...
## ..$ Month : int [1:31] 5 5 5 5 5 5 5 5 5 5 ...
## ..$ Day : int [1:31] 1 2 3 4 5 6 7 8 9 10 ...
## $ 6:'data.frame': 30 obs. of 6 variables:
## ..$ Ozone : int [1:30] NA NA NA NA NA NA 29 NA 71 39 ...
## ..$ Solar.R: int [1:30] 286 287 242 186 220 264 127 273 291 323 ...
## ..$ Wind : num [1:30] 8.6 9.7 16.1 9.2 8.6 14.3 9.7 6.9 13.8 11.5 ...
## ..$ Temp : int [1:30] 78 74 67 84 85 79 82 87 90 87 ...
## ..$ Month : int [1:30] 6 6 6 6 6 6 6 6 6 6 ...
## ..$ Day : int [1:30] 1 2 3 4 5 6 7 8 9 10 ...
## $ 7:'data.frame': 31 obs. of 6 variables:
## ..$ Ozone : int [1:31] 135 49 32 NA 64 40 77 97 97 85 ...
## ..$ Solar.R: int [1:31] 269 248 236 101 175 314 276 267 272 175 ...
## ..$ Wind : num [1:31] 4.1 9.2 9.2 10.9 4.6 10.9 5.1 6.3 5.7 7.4 ...
## ..$ Temp : int [1:31] 84 85 81 84 83 83 88 92 92 89 ...
## ..$ Month : int [1:31] 7 7 7 7 7 7 7 7 7 7 ...
## ..$ Day : int [1:31] 1 2 3 4 5 6 7 8 9 10 ...
## $ 8:'data.frame': 31 obs. of 6 variables:
## ..$ Ozone : int [1:31] 39 9 16 78 35 66 122 89 110 NA ...
## ..$ Solar.R: int [1:31] 83 24 77 NA NA NA 255 229 207 222 ...
## ..$ Wind : num [1:31] 6.9 13.8 7.4 6.9 7.4 4.6 4 10.3 8 8.6 ...
## ..$ Temp : int [1:31] 81 81 82 86 85 87 89 90 90 92 ...
## ..$ Month : int [1:31] 8 8 8 8 8 8 8 8 8 8 ...
## ..$ Day : int [1:31] 1 2 3 4 5 6 7 8 9 10 ...
## $ 9:'data.frame': 30 obs. of 6 variables:
## ..$ Ozone : int [1:30] 96 78 73 91 47 32 20 23 21 24 ...
## ..$ Solar.R: int [1:30] 167 197 183 189 95 92 252 220 230 259 ...
## ..$ Wind : num [1:30] 6.9 5.1 2.8 4.6 7.4 15.5 10.9 10.3 10.9 9.7 ...
## ..$ Temp : int [1:30] 91 92 93 93 87 84 80 78 75 73 ...
## ..$ Month : int [1:30] 9 9 9 9 9 9 9 9 9 9 ...
## ..$ Day : int [1:30] 1 2 3 4 5 6 7 8 9 10 ...Để tính mean của các collumn trong data frame theo các tháng khác nhau (airquality$Month)
lapply(s, function(x) {
colMeans(x[, c("Ozone", "Solar.R", "Wind")])
})## $`5`
## Ozone Solar.R Wind
## NA NA 11.62258
##
## $`6`
## Ozone Solar.R Wind
## NA 190.16667 10.26667
##
## $`7`
## Ozone Solar.R Wind
## NA 216.483871 8.941935
##
## $`8`
## Ozone Solar.R Wind
## NA NA 8.793548
##
## $`9`
## Ozone Solar.R Wind
## NA 167.4333 10.1800sapply() có chức năng tương tự lapply() tuy nhiên nó Cho bảng kết quả tinh gọn hơn lapply()
sapply(s, function(x) {
colMeans(x[, c("Ozone", "Solar.R", "Wind")])
})## 5 6 7 8 9
## Ozone NA NA NA NA NA
## Solar.R NA 190.16667 216.483871 NA 167.4333
## Wind 11.62258 10.26667 8.941935 8.793548 10.1800sapply(s, function(x) {
colMeans(x[, c("Ozone", "Solar.R", "Wind")], na.rm = T)
})## 5 6 7 8 9
## Ozone 23.61538 29.44444 59.115385 59.961538 31.44828
## Solar.R 181.29630 190.16667 216.483871 171.857143 167.43333
## Wind 11.62258 10.26667 8.941935 8.793548 10.18000