避免循环从r中Dataframe中的行中提取向量

Question

我在文本文件中有数据，其中案例堆叠在单个列中。我需要从每种情况中提取选定的线到向量中。我知道如何用一个循环来解析每一行，但我想知道这是否可以在R中不使用循环来完成。

下面是一个演示数据帧:

demodat <- data.frame(V1 = c(
"case01",
"sid: 112905",
"form3: 2",
"form2: 0",
"form1: An interesting comment",
"form0: 8",
"case02",
"sid: 132788",
"form3: 1",
"form2: 1",
"form1: Not sure about this",
"form0: 17",
"case03",
"sid: 102296",
"form3: 1",
"form2: 0",
"form1: This is obvious",
"form0: 12"))

下面是我用来将case, form0和form1提取为向量的循环示例:

library(tidyverse)
datlines <- 6  # Number of rows per case
case <- NA
form0 <- NA
form1 <- NA
j <- 1
for(i in 1:nrow(demodat)) {
if (str_sub(demodat[i,1],1,4)=="case") case[j] <- demodat[i,1]
#
if (str_sub(demodat[i,1],1,6)=="form0:") form0[j] <- str_replace(demodat[i,1],"form0: ","")   
if (str_sub(demodat[i,1],1,6)=="form1:") form1[j] <- str_replace(demodat[i,1],"form1: ","")      
#
if(i%%datlines == 0) j <- j + 1
}
case
form0
form1

这种方法是有效的，但是实际的数据帧有数万行，我需要从每种情况中提取许多向量。我希望找到一种更有效的方法，避免循环遍历数据帧的每一行。

我将非常感谢你的建议。

Answer 1

这是scan和grep的一个简单的基R方法。

s <- scan(textConnection(demodat$V1), what = character(), sep = ":")
s <- trimws(s)
case <- grep("case", s, value = TRUE)
form0 <- s[grep("form0", s) + 1L]
form1 <- s[grep("form1", s) + 1L]
rm(s)
case
#> [1] "case01" "case02" "case03"
form0
#> [1] "8"  "17" "12"
form1
#> [1] "An interesting comment" "Not sure about this"    "This is obvious"

^{在2022-05-06由reprex包(v2.0.1)创建}

Answer 2

library(dplyr)
library(tidyr)
demodat %>%
separate_rows(V1, sep = ',') %>% ## one row per ','-separated term
separate(V1, into = c('parameter', 'value'), sep = ':') ## (1) 
## (1) now you can filter for parameter, e.g. 'sid' or grepl('case', parameter)

输出:

## # A tibble: 18 x 2
##    parameter value                    
##    <chr>     <chr>                    
##  1 case01     NA                      
##  2 sid       " 112905"                
##  3 form3     " 2"                     
##  4 form2     " 0"                     
##  5 form1     " An interesting comment"
##  6 form0     " 8"                     
##  7 case02     NA       
## ...

编辑要跟踪case ID，请在管道中添加以下内容:

## ... %>%
mutate(case_id = ifelse(grepl('case', parameter),
gsub('^case(.*)$','\1',parameter),
NA)
) %>%
fill(case_id, .direction = 'down')

Answer 3

另一个基数:

demo2 <- read.dcf(textConnection(gsub('case*', 'case*: ', demodat$V1)), all = TRUE)
> demo2
case*                    sid   form3   form2
1 01, 02, 03 112905, 132788, 102296 2, 1, 1 0, 1, 0
form1     form0
1 An interesting comment, Not sure about this, This is obvious 8, 17, 12
> class(demo2)
[1] "data.frame"