(这是之前发布在 data-table-help mailing list 上的,但已经有几个星期没有评论了,我做了更多的尝试来调试它。)
我遇到了一个奇怪的错误,互联网搜索仅出现在 data.table
的提交日志中:
# Error in dcast.data.table(test.table, as.formula(paste(class.col, "+", :
# retFirst must be integer vector the same length as nrow(i)
这是在我通过随机重采样Trial
并替换的data.table上运行先前测试的工作dcast.data.table表达式时出现的。有问题的部分是这样的:
dcast.data.table(test.table,
Class + Time + Trial ~ Channel,
value.var = "Voltage",
fun.aggregate=identity)
它似乎被输入表中接近重复的行所阻塞(即,无论表中存在或不存在 id
列,错误都是相同的):
test.table <- structure(list(Trial = c(1169L, 1169L), Sample = c(155L, 155L
), Class = c(1L, 1L), Subject = structure(c(13L, 13L), .Label = c("s01",
"s02", "s03", "s04", "s05", "s06", "s07", "s08", "s09", "s10",
"s11", "s12", "s13"), class = "factor"), Channel = c(1L, 1L),
Voltage = structure(c(-0.992322316444497, -0.992322316444497
), "`scaled:center`" = -6.23438399446429e-16, "`scaled:scale`" = 1),
Time = c(201.149466192171, 201.149466192171), Baseline = c(0.688151312347969,
0.688151312347969), id = 1:2), .Names = c("Trial", "Sample",
"Class", "Subject", "Channel", "Voltage", "Time", "Baseline",
"id"), class = c("data.table", "data.frame"), row.names = c(NA,
-2L), sorted = "id")
test.table
# Trial Sample Class Subject Channel Voltage Time Baseline id
# 1: 1169 155 1 s13 1 -0.9923223 201.1495 0.6881513 1
# 2: 1169 155 1 s13 1 -0.9923223 201.1495 0.6881513 2
dcast.data.table(test.table,
Class + Time + Trial ~ Channel,
value.var = "Voltage",
fun.aggregate=identity)
# Error in dcast.data.table(test.table, Class + Time + Trial ~ Channel, :
# retFirst must be integer vector the same length as nrow(i)
更改 dcast
公式中的单个列接近我正在寻找的输出:
test.table[2,Trial:=1170]
dcast.data.table(test.table,
Class + Time + Trial ~ Channel,
value.var = "Voltage",
fun.aggregate=identity)
# Class Time Trial 1
# 1: 1 201.1495 1169 -0.9923223
# 2: 1 201.1495 1170 -0.9923223
什么困扰了 data.table?我尝试更改键并打乱公式术语的顺序只是为了看看,因为我不明白这个错误,但这不起作用。
如果我用 reshape2
中的常规 dcast
替换函数调用,我会收到一个看似不相关的错误:
# Error in vapply(indices, fun, .default) : values must be length 0, but FUN(X[[29]]) result is length 1
此时,在我的代码中,我不关心 Trial
值是否正确,因此我可以通过在公式中将其替换为 id
来解决此问题,但我对更通用或更强大的解决方案感兴趣。
最佳答案
更新:在 commit 1253 中修复v1.9.3 的。来自 NEWS :
dcast.data.table
provides better error message whenfun.aggregate
is specified but it returns length != 1. Closes git #693. Thanks to Trevor Alexander for reporting here on SO.
我同意错误消息应该更有助于理解问题,并且通常位于 data.table 中。这只是我没有预见到的情况。
如果可以的话请提交问题 here作为一个错误,我会在有时间的时候修复它。
然而,你的问题对我来说似乎是微不足道的 RTFM。来自 ?dcast.data.table
:
fun.aggregate
- Should the data be aggregated before casting? If the formula doesn't identify single observation for each cell, then aggregation defaults to length with a message.In the DETAILS section: "... fun.aggregate will have to be used. The aggregating function should take a vector as input and return a single value (or a list of length one) as output." ...
在您的示例中,公式的 LHS 会产生两个相同的行,这意味着必须使用 fun.aggregate
- 如果您不使用,则默认为 length
一个(就像 reshape2:::dcast
那样)。并且您已经使用了identity
,它只会返回值。因此它返回了 Voltage
的两个值,这是该函数不喜欢的。
错误消息应该类似于:
Error:
fun.aggregate
should return, for each unique group (from formula'sLHS
), a length 1 vector, but returnslength=2
for a group.
或者类似的东西。请随意建议更好/更清晰的错误消息。
PS:我不明白你所说的“接近重复”是什么意思。
identical(test.table[1, list(Class, Time, Trial)],
test.table[2, list(Class, Time, Trial)])
# [1] TRUE
如果您在 LHS 上使用 id
列,那么您应该能够获得所需的结果,因为您现在可以唯一地标识行...
dcast.data.table(test.table,
Class + Time + Trial ~ Channel + id,
value.var = "Voltage",
fun.aggregate=identity)
# Class Time Trial 1_1 1_2
# 1: 1 201.1495 1169 -0.9923223 -0.9923223
该函数仅考虑公式 LHS 中给出的列来确定是否存在唯一行,而不考虑实际输入数据是否具有唯一行(如果这是混淆的话)。
回答OP的第二条评论:
当前获得结果(没有错误)的唯一方法是您的函数返回一个列表:
dcast.data.table(test.table,
Class + Time + Trial ~ Channel,
value.var = "Voltage",
fun.aggregate=list)
# Class Time Trial 1
# 1: 1 201.1495 1169 -0.9923223,-0.9923223
然后您可以检查列的长度是否全部为 1,如果是,则取消列出。
关于r - dcast.data.table 中未记录的错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/24152733/