对名称中具有特定模式的列进行行求和 [英] Row sums over columns with a certain pattern in their name
本文介绍了对名称中具有特定模式的列进行行求和的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我有一个这样的data.table
I have a data.table like this
dput(DT)
structure(list(ref = c(3L, 3L, 3L, 3L), nb = 12:15, i1 = c(3.1e-05,
0.044495, 0.82244, 0.322291), i2 = c(0.000183, 0.155732, 0.873416,
0.648545), i3 = c(0.000824, 0.533939, 0.838542, 0.990648), i4 = c(0.044495,
0.82244, 0.322291, 0.393595)), .Names = c("ref", "nb", "i1",
"i2", "i3", "i4"), row.names = c(NA, -4L), class = c("data.table",
"data.frame"), .internal.selfref = <pointer: 0x0000000000320788>)
DT
# ref nb i1 i2 i3 i4
# 1: 3 12 0.000031 0.000183 0.000824 0.044495
# 2: 3 13 0.044495 0.155732 0.533939 0.822440
# 3: 3 14 0.822440 0.873416 0.838542 0.322291
# 4: 3 15 0.322291 0.648545 0.990648 0.393595
现在我想计算行总和,但只包括以i"开头的列.(i1"、i2"等)
Now I want to calculate rows sums, but only including columns which start with an "i" ("i1", "i2", etc)
我已经使用 grep
创建了一个包含要求和的列名的向量:
I have used grep
to create a vector of the column names to be summed:
listCol <- colnames(DT)[grep("i", colnames(DT))]
listCol
# [1] "i1" "i2" "i3" "i4"
然后我尝试遍历列:
DT$sum <- rep.int(0, nrow(DT))
for (i in listCol){
DT$sum = DT$sum + DT[ , get(i)]
}
...给出所需的输出:
...which gives the desired output:
DT
# ref nb i1 i2 i3 i4 sum
# 1: 3 12 0.000031 0.000183 0.000824 0.044495 0.045533
# 2: 3 13 0.044495 0.155732 0.533939 0.822440 1.556606
# 3: 3 14 0.822440 0.873416 0.838542 0.322291 2.856689
# 4: 3 15 0.322291 0.648545 0.990648 0.393595 2.355079
如何改进我的代码?
这个子问题包括前一个问题的部分答案:
This sub-question includes partially the answer to the previous one :
如何避免这种奇怪的符号:
How to avoid this kind of strange notation :
myrowMeans = function (x){
rowMeans(x, na.rm = TRUE)
}
DT[ , var := myrowMeans(.SD-myrowMeans(.SD)^2), .SDcols = grep("i", colnames(DT))]
推荐答案
你也可以试试Reduce
DT[, Sum := Reduce(`+`, .SD), .SDcols=listCol][]
# ref nb i1 i2 i3 i4 Sum
#1: 3 12 0.000031 0.000183 0.000824 0.044495 0.045533
#2: 3 13 0.044495 0.155732 0.533939 0.822440 1.556606
#3: 3 14 0.822440 0.873416 0.838542 0.322291 2.856689
#4: 3 15 0.322291 0.648545 0.990648 0.393595 2.355079
注意:如果有NA"值,应在Reduce
之前用0"替换,即
NOTE: If there are "NA" values, it should be replaced with '0' before Reduce
i.e.
DT[, Sum := Reduce(`+`, lapply(.SD, function(x) replace(x,
which(is.na(x)), 0))), .SDcols=listCol][]
**另一种解决方案:**使用 rowSums
**Another solution :**using rowSums
DT[, Sum := rowSums(.SD, na.rm = TRUE), .SDcols = grep("i", names(DT))]
这篇关于对名称中具有特定模式的列进行行求和的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文