从文档中我读到了invisible() returns a (temporarily) invisible copy of an object。现在，当我使用隐形时，我总是需要在实际打印之前调用对象两次。
我使用data.table并希望我的函数返回一个对象的不可见副本，因为满足某个条件（即函数的过早中止）。
我注意到，如果在另一个函数中使用了隐形返回的对象，那么“需要double / two调用”的这种行为也适用，使得它的使用看似无法使用。是什么导致这种行为？难道我做错了什么？如何让函数无形地返回，并在第一次调用时打印？
请参阅以下示例代码：
example <- function(DT) {
if (!(1 %in% DT$RSI.verticalBottom) | !(1 %in% DT$RSI.top)) {
# abort if there is no buy or sell signal
DT[, `:=`(pos = NA,
return = NA
)]
return(invisible(DT))
}
> example(sample.data)
> sample.data
> sample.data
conm tic datadate cshoq gind year month yearmon fdateq pdateq fyr fyearq fqtr
1: NS GROUP INC NSS.1 2000-01-31 NA 101010 2000 1 2000_1 NA <NA> NA NA NA
2: NS GROUP INC NSS.1 2000-02-29 NA 101010 2000 2 2000_2 NA <NA> NA NA NA
3: NS GROUP INC NSS.1 2000-03-31 21.533 101010 2000 3 2000_3 NA <NA> 9 2000 2
4: NS GROUP INC NSS.1 2000-04-30 NA 101010 2000 4 2000_4 NA <NA> NA NA NA
5: NS GROUP INC NSS.1 2000-05-31 NA 101010 2000 5 2000_5 NA <NA> NA NA NA
6: NS GROUP INC NSS.1 2000-06-30 22.008 101010 2000 6 2000_6 NA <NA> 9 2000 3
req epspiq epspxq ajexq saleq saley ivncfy gsubind dpq ibmiiq ibq iby oiadpq
1: NA NA NA NA NA NA NA NA NA NA NA NA NA
2: NA NA NA NA NA NA NA NA NA NA NA NA NA
3: -58.396 -0.38 -0.38 1 100.107 186.733 10.77 10101020 5.517 NA -8.231 -21.165 -5.617
4: NA NA NA NA NA NA NA NA NA NA NA NA NA
5: NA NA NA NA NA NA NA NA NA NA NA NA NA
6: -63.168 -0.19 -0.23 1 73.652 260.385 20.90 10101020 NA NA -5.048 -26.213 NA
oiadpy oibdpq oibdpy xiq xoprq cogsy dlcchy wcapchy QEBIT.adep YEBIT.adep QEBIT.bdep
1: NA NA NA NA NA NA NA NA NA NA NA
2: NA NA NA NA NA NA NA NA NA NA NA
3: -16.924 -0.1 -5.57 0 100.207 177.826 -0.394 NA -0.05610996 -0.09063208 -0.0009989311
4: NA NA NA NA NA NA NA NA NA NA NA
5: NA NA NA NA NA NA NA NA NA NA NA
6: NA NA NA 0 NA NA -0.394 NA NA NA NA
YEBIT.bdep QEBT YEBT f_id I.QSales IWA.QEBIT IWA.QEBT I.YSales IWA.YEBIT
1: NA NA NA NA NA NA NA NA NA
2: NA NA NA NA NA NA NA NA NA
3: -0.000535524 -0.08222202 -0.1133437 2000Q2 19344.53 0.08160277 0.03577741 196223.7 0.08329726
4: NA NA NA NA NA NA NA NA NA
5: NA NA NA NA NA NA NA NA NA
6: NA -0.06853853 -0.1006702 2000Q3 19798.64 0.10680607 0.06096211 196223.7 0.08329726
IWA.YEBT QSales.pc YSales.pc RSI_QEBIT RSI_QEBT RSI_IWA.QEBIT RSI_IWA.QEBT adj.factor
1: NA NA NA NA NA NA NA 1
2: NA NA NA NA NA NA NA 1
3: 0.03875869 0.005174952 0.0009516334 41.45963 32.93934 29.96487 18.23527 1
4: NA NA NA NA NA NA NA 1
5: NA NA NA NA NA NA NA 1
6: 0.03875869 0.003720053 0.0013269806 49.83110 34.64800 37.58678 24.75847 1
dvpsxm cshtrm curcdm close high low trfm trt1m close.unAdj mktcap close.div
1: NA 4557500 USD 8.8750 10.1250 6.7500 1.0409 16.3934 8.8750 NA 8.8750
2: NA 4506100 USD 11.6875 12.1250 8.0625 1.0409 31.6901 11.6875 NA 11.6875
3: NA 4146200 USD 16.3125 16.8125 11.3750 1.0409 39.5722 16.3125 351.2571 16.3125
4: NA 3215400 USD 15.8750 16.3750 12.8750 1.0409 -2.6820 15.8750 NA 15.8750
5: NA 2948800 USD 18.3125 19.3750 16.0625 1.0409 15.3543 18.3125 NA 18.3125
6: NA 4296100 USD 20.9375 21.0000 17.7500 1.0409 14.3345 20.9375 460.7925 20.9375
RSI_close RSI.verticalBottom RSI.top return pos
1: NA NA NA NA NA
2: NA NA NA NA NA
3: NA NA NA NA NA
4: NA NA NA NA NA
5: NA NA NA NA NA
6: NA NA NA NA NA
示例数据
> dput(sample.data)
structure(list(conm = c("NS GROUP INC", "NS GROUP INC", "NS GROUP INC",
"NS GROUP INC", "NS GROUP INC", "NS GROUP INC"), tic = c("NSS.1",
"NSS.1", "NSS.1", "NSS.1", "NSS.1", "NSS.1"), datadate = structure(c(10987,
11016, 11047, 11077, 11108, 11138), class = "Date"), cshoq = c(NA,
NA, 21.533, NA, NA, 22.008), gind = c(101010L, 101010L, 101010L,
101010L, 101010L, 101010L), year = c(2000, 2000, 2000, 2000,
2000, 2000), month = c(1, 2, 3, 4, 5, 6), yearmon = c("2000_1",
"2000_2", "2000_3", "2000_4", "2000_5", "2000_6"), fdateq = c(NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_
), pdateq = structure(c(NA_real_, NA_real_, NA_real_, NA_real_,
NA_real_, NA_real_), class = "Date"), fyr = c(NA, NA, 9L, NA,
NA, 9L), fyearq = c(NA, NA, 2000L, NA, NA, 2000L), fqtr = c(NA,
NA, 2L, NA, NA, 3L), req = c(NA, NA, -58.396, NA, NA, -63.168
), epspiq = c(NA, NA, -0.38, NA, NA, -0.19), epspxq = c(NA, NA,
-0.38, NA, NA, -0.23), ajexq = c(NA, NA, 1, NA, NA, 1), saleq = c(NA,
NA, 100.107, NA, NA, 73.652), saley = c(NA, NA, 186.733, NA,
NA, 260.385), ivncfy = c(NA, NA, 10.77, NA, NA, 20.9), gsubind = c(NA,
NA, 10101020L, NA, NA, 10101020L), dpq = c(NA, NA, 5.517, NA,
NA, NA), ibmiiq = c(NA_real_, NA_real_, NA_real_, NA_real_, NA_real_,
NA_real_), ibq = c(NA, NA, -8.231, NA, NA, -5.048), iby = c(NA,
NA, -21.165, NA, NA, -26.213), oiadpq = c(NA, NA, -5.617, NA,
NA, NA), oiadpy = c(NA, NA, -16.924, NA, NA, NA), oibdpq = c(NA,
NA, -0.1, NA, NA, NA), oibdpy = c(NA, NA, -5.57, NA, NA, NA),
xiq = c(NA, NA, 0, NA, NA, 0), xoprq = c(NA, NA, 100.207,
NA, NA, NA), cogsy = c(NA, NA, 177.826, NA, NA, NA), dlcchy = c(NA,
NA, -0.394, NA, NA, -0.394), wcapchy = c(NA_real_, NA_real_,
NA_real_, NA_real_, NA_real_, NA_real_), QEBIT.adep = c(NA,
NA, -0.0561099623402959, NA, NA, NA), YEBIT.adep = c(NA,
NA, -0.0906320789576561, NA, NA, NA), QEBIT.bdep = c(NA,
NA, -0.000998931143676266, NA, NA, NA), YEBIT.bdep = c(NA,
NA, -0.000535523983441598, NA, NA, NA), QEBT = c(NA, NA,
-0.0822220224359935, NA, NA, -0.0685385325585184), YEBT = c(NA,
NA, -0.113343651095414, NA, NA, -0.100670161491637), f_id = c(NA,
NA, "2000Q2", NA, NA, "2000Q3"), I.QSales = c(NA, NA, 19344.526,
NA, NA, 19798.641), IWA.QEBIT = c(NA, NA, 0.0816027748625115,
NA, NA, 0.10680606815387), IWA.QEBT = c(NA, NA, 0.0357774080378087,
NA, NA, 0.0609621135107203), I.YSales = c(NA, NA, 196223.665,
NA, NA, 196223.665), IWA.YEBIT = c(NA, NA, 0.0832972567299668,
NA, NA, 0.0832972567299668), IWA.YEBT = c(NA, NA, 0.0387586889685299,
NA, NA, 0.0387586889685299), QSales.pc = c(NA, NA, 0.00517495233535316,
NA, NA, 0.00372005331072976), YSales.pc = c(NA, NA, 0.000951633433204909,
NA, NA, 0.00132698061673652), RSI_QEBIT = c(NA, NA, 41.4596290506163,
NA, NA, 49.8310957229999), RSI_QEBT = c(NA, NA, 32.939339100869,
NA, NA, 34.6480049470139), RSI_IWA.QEBIT = c(NA, NA, 29.9648696052066,
NA, NA, 37.5867809473848), RSI_IWA.QEBT = c(NA, NA, 18.2352737965041,
NA, NA, 24.7584711404174), adj.factor = c(1, 1, 1, 1, 1,
1), dvpsxm = c(NA_real_, NA_real_, NA_real_, NA_real_, NA_real_,
NA_real_), cshtrm = c(4557500, 4506100, 4146200, 3215400,
2948800, 4296100), curcdm = c("USD", "USD", "USD", "USD",
"USD", "USD"), close = c(8.875, 11.6875, 16.3125, 15.875,
18.3125, 20.9375), high = c(10.125, 12.125, 16.8125, 16.375,
19.375, 21), low = c(6.75, 8.0625, 11.375, 12.875, 16.0625,
17.75), trfm = c(1.0409, 1.0409, 1.0409, 1.0409, 1.0409,
1.0409), trt1m = c(16.3934, 31.6901, 39.5722, -2.682, 15.3543,
14.3345), close.unAdj = c(8.875, 11.6875, 16.3125, 15.875,
18.3125, 20.9375), mktcap = c(NA, NA, 351.2570625, NA, NA,
460.7925), close.div = c(8.875, 11.6875, 16.3125, 15.875,
18.3125, 20.9375), RSI_close = c(NA_real_, NA_real_, NA_real_,
NA_real_, NA_real_, NA_real_), RSI.verticalBottom = c(NA_real_,
NA_real_, NA_real_, NA_real_, NA_real_, NA_real_), RSI.top = c(NA_real_,
NA_real_, NA_real_, NA_real_, NA_real_, NA_real_), return = c(NA,
NA, NA, NA, NA, NA), pos = c(NA, NA, NA, NA, NA, NA)), .Names = c("conm",
"tic", "datadate", "cshoq", "gind", "year", "month", "yearmon",
"fdateq", "pdateq", "fyr", "fyearq", "fqtr", "req", "epspiq",
"epspxq", "ajexq", "saleq", "saley", "ivncfy", "gsubind", "dpq",
"ibmiiq", "ibq", "iby", "oiadpq", "oiadpy", "oibdpq", "oibdpy",
"xiq", "xoprq", "cogsy", "dlcchy", "wcapchy", "QEBIT.adep", "YEBIT.adep",
"QEBIT.bdep", "YEBIT.bdep", "QEBT", "YEBT", "f_id", "I.QSales",
"IWA.QEBIT", "IWA.QEBT", "I.YSales", "IWA.YEBIT", "IWA.YEBT",
"QSales.pc", "YSales.pc", "RSI_QEBIT", "RSI_QEBT", "RSI_IWA.QEBIT",
"RSI_IWA.QEBT", "adj.factor", "dvpsxm", "cshtrm", "curcdm", "close",
"high", "low", "trfm", "trt1m", "close.unAdj", "mktcap", "close.div",
"RSI_close", "RSI.verticalBottom", "RSI.top", "return", "pos"
), sorted = c("conm", "tic", "datadate", "cshoq", "gind", "year",
"month", "yearmon"), class = c("data.table", "data.frame"), row.names = c(NA,
-6L), .internal.selfref = <pointer: 0x102806978>)