ddply具有固定的行数 [英] ddply with fixed number of rows

问题描述

我想按行数"分解数据.也就是说，我想向函数发送固定数量的行，并且当我到达数据帧的末尾(最后一个块)时，无论是否具有固定的行数或更少的行数，我都只需要发送该块.像这样:

I want to break up my data by 'number of rows'. That is to say I want to send a fixed number of rows to my function and when I get to the end of the data frame (last chunk) I need to just send the chunk whether it has the fixed number of rows or less. Something like this:

ddply(df, .(8 rows), .fun=somefunction)

推荐答案

如果要使用plyr，则可以添加类别列:

If you want to use plyr you can add a category column:

df <- data.frame(x=rnorm(100), y=rnorm(100))

somefunction <- function(df) {
    data.frame(mean(df$x), mean(df$y))
}

df$category <- rep(letters[1:10], each=10)

ddply(df, .(category), somefunction)

但是，在这种情况下，申请家庭可能是一个更好的选择:

But, the apply family might be a better option in this case:

somefunction <- function(n, x, y) {
    data.frame(mean(x[n:(n+9)]), mean(y[n:n+9]))
}

lapply(seq(1, nrow(df), by=10), somefunction, x=df$x, y=df$y)

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