对列组应用函数 [英] apply a function over groups of columns
问题描述
我如何使用 apply 或相关函数来创建一个新的数据框，其中包含一个非常大的数据框中每对列的行平均值的结果?
How can I use apply or a related function to create a new data frame that contains the results of the row averages of each pair of columns in a very large data frame?
我有一个仪器可以输出 n 对大量样本的重复测量值，其中每个测量值都是一个向量(所有测量值都是相同的长度向量).我想计算每个样本的所有重复测量的平均值(和其他统计数据).这意味着我需要将 n 连续列组合在一起并进行逐行计算.
I have an instrument that outputs n replicate measurements on a large number of samples, where each single measurement is a vector (all measurements are the same length vectors). I'd like to calculate the average (and other stats) on all replicate measurements of each sample. This means I need to group n consecutive columns together and do row-wise calculations.
举一个简单的例子，对两个样本进行三次重复测量，我如何最终得到一个有两列(每个样本一列)的数据框，其中一列是 dat 中每行重复的平均值$a、dat$b 和 dat$c 以及 dat$d 每一行的平均值，dat$e 和 dat$f.
For a simple example, with three replicate measurements on two samples, how can I end up with a data frame that has two columns (one per sample), one that is the average each row of the replicates in dat$a, dat$b and dat$c and one that is the average of each row for dat$d, dat$e and dat$f.
这是一些示例数据
dat <- data.frame( a = rnorm(16), b = rnorm(16), c = rnorm(16), d = rnorm(16), e = rnorm(16), f = rnorm(16))
a b c d e f
1 -0.9089594 -0.8144765 0.872691548 0.4051094 -0.09705234 -1.5100709
2 0.7993102 0.3243804 0.394560355 0.6646588 0.91033497 2.2504104
3 0.2963102 -0.2911078 -0.243723116 1.0661698 -0.89747522 -0.8455833
4 -0.4311512 -0.5997466 -0.545381175 0.3495578 0.38359390 0.4999425
5 -0.4955802 1.8949285 -0.266580411 1.2773987 -0.79373386 -1.8664651
6 1.0957793 -0.3326867 -1.116623982 -0.8584253 0.83704172 1.8368212
7 -0.2529444 0.5792413 -0.001950741 0.2661068 1.17515099 0.4875377
8 1.2560402 0.1354533 1.440160168 -2.1295397 2.05025701 1.0377283
9 0.8123061 0.4453768 1.598246016 0.7146553 -1.09476532 0.0600665
10 0.1084029 -0.4934862 -0.584671816 -0.8096653 1.54466019 -1.8117459
11 -0.8152812 0.9494620 0.100909570 1.5944528 1.56724269 0.6839954
12 0.3130357 2.6245864 1.750448404 -0.7494403 1.06055267 1.0358267
13 1.1976817 -1.2110708 0.719397607 -0.2690107 0.83364274 -0.6895936
14 -2.1860098 -0.8488031 -0.302743475 -0.7348443 0.34302096 -0.8024803
15 0.2361756 0.6773727 1.279737692 0.8742478 -0.03064782 -0.4874172
16 -1.5634527 -0.8276335 0.753090683 2.0394865 0.79006103 0.5704210
我在做这样的事情
X1 X2
1 -0.28358147 -0.40067128
2 0.50608365 1.27513471
3 -0.07950691 -0.22562957
4 -0.52542633 0.41103139
5 0.37758930 -0.46093340
6 -0.11784382 0.60514586
7 0.10811540 0.64293184
8 0.94388455 0.31948189
9 0.95197629 -0.10668118
10 -0.32325169 -0.35891702
11 0.07836345 1.28189698
12 1.56269017 0.44897971
13 0.23533617 -0.04165384
14 -1.11251880 -0.39810121
15 0.73109533 0.11872758
16 -0.54599850 1.13332286
我用这个做了，但显然对我更大的数据框没有好处......
which I did with this, but is obviously no good for my much larger data frame...
data.frame(cbind(
apply(cbind(dat$a, dat$b, dat$c), 1, mean),
apply(cbind(dat$d, dat$e, dat$f), 1, mean)
))
我已经尝试了 apply 和循环，但无法完全整合.我的实际数据有数百列.
I've tried apply and loops and can't quite get it together. My actual data has some hundreds of columns.
推荐答案
这可能更适用于您传递索引列表的情况.如果速度是一个问题(大数据帧)，我会选择 lapply 和 do.call 而不是 sapply:
This may be more generalizable to your situation in that you pass a list of indices. If speed is an issue (large data frame) I'd opt for lapply with do.call rather than sapply:
x <- list(1:3, 4:6)
do.call(cbind, lapply(x, function(i) rowMeans(dat[, i])))
如果您也只有列名也可以使用:
Works if you just have col names too:
x <- list(c('a','b','c'), c('d', 'e', 'f'))
do.call(cbind, lapply(x, function(i) rowMeans(dat[, i])))
编辑
只是碰巧想也许您想自动执行此操作以每三列执行一次.我知道有更好的方法，但这里是一个 100 列的数据集:
Just happened to think maybe you want to automate this to do every three columns. I know there's a better way but here it is on a 100 column data set:
dat <- data.frame(matrix(rnorm(16*100), ncol=100))
n <- 1:ncol(dat)
ind <- matrix(c(n, rep(NA, 3 - ncol(dat)%%3)), byrow=TRUE, ncol=3)
ind <- data.frame(t(na.omit(ind)))
do.call(cbind, lapply(ind, function(i) rowMeans(dat[, i])))
编辑 2仍然对索引不满意.我认为有一种更好/更快的方法来传递索引.这是第二种虽然不令人满意的方法:
EDIT 2 Still not happy with the indexing. I think there's a better/faster way to pass the indexes. here's a second though not satisfying method:
n <- 1:ncol(dat)
ind <- data.frame(matrix(c(n, rep(NA, 3 - ncol(dat)%%3)), byrow=F, nrow=3))
nonna <- sapply(ind, function(x) all(!is.na(x)))
ind <- ind[, nonna]
do.call(cbind, lapply(ind, function(i)rowMeans(dat[, i])))
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