滚动文本与R中的Data.Table连接
我有一个如下所示的数据集:滚动文本与R中的Data.Table连接,r,data.table,R,Data.table,我有一个如下所示的数据集: rownum<-c(1,2,3,4,5,6,7,8,9,10) name<-c("jeff","jeff","mary","jeff","jeff","jeff","mary","mary","mary","mary") text<-c("a","b","c","d","e","f","g","h","i","j") a<-data.table(rownum,name,text) rownum您可以使用Reduce和accumulate选项:
rownum<-c(1,2,3,4,5,6,7,8,9,10)
name<-c("jeff","jeff","mary","jeff","jeff","jeff","mary","mary","mary","mary")
text<-c("a","b","c","d","e","f","g","h","i","j")
a<-data.table(rownum,name,text)
rownum您可以使用Reduce
和accumulate
选项:
a[, rolltext := Reduce(paste0, text, accumulate = TRUE), by = name]
rownum name text rolltext
1: 1 jeff a a
2: 2 jeff b ab
3: 3 mary c c
4: 4 jeff d abd
5: 5 jeff e abde
6: 6 jeff f abdef
7: 7 mary g cg
8: 8 mary h cgh
9: 9 mary i cghi
10: 10 mary j cghij
或者,正如@DavidArenburg所建议的,使用sapply
构造每一行:
a[, rolltext := sapply(1:.N, function(x) paste(text[1:x], collapse = '')), by = name]
这是一个连续求和,而滚动求和(在OP的标题中)则有所不同,至少在R术语中是这样。这里有一个使用substring()的想法
给
rownum name text rolltext
1: 1 jeff a a
2: 2 jeff b ab
3: 3 mary c c
4: 4 jeff d abd
5: 5 jeff e abde
6: 6 jeff f abdef
7: 7 mary g cg
8: 8 mary h cgh
9: 9 mary i cghi
10: 10 mary j cghij
我们也许可以通过stringi软件包来加快速度
美好的也可以a[,rolltext:=sappy(1:N,函数(x)粘贴(text[1:x],collapse=''),by=name]
谢谢,David,我已经在中编辑过了。这样做的缺点可能是它需要更多的粘贴(sum(seq(.N)-1)
vs.N-1
withReduce
)。无论如何,这是我的直觉/猜测。
a[, rolltext := substring(paste(text, collapse = ""), 1, 1:.N), by = name]
rownum name text rolltext
1: 1 jeff a a
2: 2 jeff b ab
3: 3 mary c c
4: 4 jeff d abd
5: 5 jeff e abde
6: 6 jeff f abdef
7: 7 mary g cg
8: 8 mary h cgh
9: 9 mary i cghi
10: 10 mary j cghij
library(stringi)
a[, rolltext := stri_sub(stri_c(text, collapse = ""), length = 1:.N), by = name]