R 环路中的子集ffdf

我正在尝试使用ffbase在循环中子集一个非常大的ffdf对象，但是我得到了错误消息：

Error in UseMethod("as.hi") : no applicable method for 'as.hi' applied to an object of
class "NULL"

我在ssh上运行这段代码，并且有大量可用内存。下面是我试图运行的代码：

# totalD is an ffdf with columns ID, TS, and TD, each with 288,133,589 rows. ID consists
# of integers. TS is a column of integer timestamps with second precision. TD is of type
# double. Uid3 is an integer vector consisting of the 1205 unique entries of totalD$ID.

# H_times creates a matrix of the sum of the entries in TD traveled in each hour
H_times <- function(totalD, Uid3) {

    # hours is the number of unique hours of the experiment
    hours <- length(unique(subset(totalD$TS, totalD$TS %% 3600 == 0)))-1

    # bH is used as a counter in a the following loops
    bH <- min(unique(subset(totalD$TS, totalD$TS %% 3600 == 0)))

    # sum_D_matrix is the output
    sum_D_matrix <- matrix(0, nrow = hours, ncol = length(Uid3))

    for(i in 1:length(Uid3)) {
        Bh <- bH
        for(j in 1:hours) {
            sum_D_matrix[j,i] <- sum(subset(totalD$TD, totalD$TS >= Bh & totalD$TS < (Bh + 3600) & totalD$ID == Uid3[i]))
            Bh <- Bh + 3600
        }
    }
    save(sum_D_matrix, file = "sum_D_matrix)
}

H_times(totalD, Uid3)

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我试图实现jwijffels在问题评论中建议的修复，但没有效果。提前谢谢

这是由线路引起的：

sum_D_matrix[j,i] <- sum(subset(totalD$TD, 
    totalD$TS >= Bh & totalD$TS < (Bh + 3600) & totalD$ID == Uid3[i]))

当生成的向量为空时，FFT返回NULL，正如我提到的，它不能返回长度为0的向量

旁注

您使用子集的方式实际上有点奇怪。使用子集的原因之一是通过去掉所有的totalD$来简化表示法。更“常用”的使用方式是：

sum_D_matrix[j,i] <- sum(subset(totalD, TS >= Bh & TS < (Bh + 3600) & ID == Uid3[i], 
    TD, drop=TRUE))

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谢谢当我使用你的代码和它的变体时，我得到了一个错误，其中“which”的chevale，nl，envir:argument是不符合逻辑的。

sum_D_matrix[j,i] <- sum(subset(totalD, TS >= Bh & TS < (Bh + 3600) & ID == Uid3[i], 
    TD, drop=TRUE))