通过堆叠器的一些努力和帮助,我能够解析网页并将其保存为数据帧。我想在多个xml文件上重复相同的操作并对列表进行rbind。这是我尝试并成功做到的:
library(XML)
xml.url <- "http://www.ebi.ac.uk/ena/data/view/ERS445758&display=xml"
doc <- xmlParse(xml.url)
x <- xmlToDataFrame(getNodeSet(doc,"//SAMPLE_ATTRIBUTE"))
x$UNITS <- NULL
x_t <- t(x)
x_t <- as.data.frame(x_t)
names(x_t) <- as.matrix(x_t[1, ])
x_t <- x_t[-1, ]
x_t[] <- lapply(x_t, function(x) type.convert(as.character(x)))
以上代码运行良好,现在当我尝试应用函数对多个xml文件执行相同操作时:
ERS_ID <- c("ERS445758","ERS445759", "ERS445760", "ERS445761", "ERS445762")
xml_url_test = as.vector(sprintf("http://www.ebi.ac.uk/ena/data/view/ERS445758&display=xml",
ERS_ID))
XML_parser <- function(XML_url){
doc <- xmlParse(XML_url)
x <- xmlToDataFrame(getNodeSet(doc,"//SAMPLE_ATTRIBUTE"))
x$UNITS <- NULL
x_t <- t(x)
x_t <- as.data.frame(x_t)
names(x_t) <- as.matrix(x_t[1, ])
x_t <- x_t[-1, ]
x_t[] <- lapply(x_t, function(x) type.convert(as.character(x)))
return(x_t)
}
major_test <- sapply(xml_url_test, XML_parser)
它可以工作,但是给了我一个很长的列表,它不是我为单个XML文件生成的正确的数据帧格式。
最后,我还想在最终数据框中添加一列,其中包含ERS_ID向量中的ERS编号
类似函数中的x_t$ERSid <- ERS_ID
有人可以指出我在功能中缺少什么,以及更好的方法来完成任务吗?
谢谢!
答案 0 :(得分:3)
你的主要问题是使用sapply
而不是lapply()
,其中后者返回一个列表,之前尝试简化为向量或矩阵,这里是一个矩阵。
major_test <- lapply(xml_url_test, XML_parser)
当然,sapply
是lapply
的包装,也可以返回一个列表:sapply(..., simplify=FALSE)
:
major_test <- sapply(xml_url_test, XML_parser, simplify=FALSE)
但是,其他一些项目出现了:
%s
运算符将 ERS_ID 连接到网址。所以现在,相同的网址正在重复。gsub
删除 ERS 前缀。R 代码(已调整)
XML_parser <- function(eid) {
XML_url <- as.vector(sprintf("http://www.ebi.ac.uk/ena/data/view/%s&display=xml", eid))
doc <- xmlParse(XML_url)
x <- xmlToDataFrame(getNodeSet(doc,"//SAMPLE_ATTRIBUTE"))
x$UNITS <- NULL
x_t <- t(x)
x_t <- as.data.frame(x_t)
names(x_t) <- as.matrix(x_t[1, ])
x_t <- x_t[-1, ]
x_t[] <- lapply(x_t, function(x) type.convert(as.character(x)))
x_t$ERSid <- gsub("ERS", "", eid) # ADD COL, REMOVE ERS
x_t <- x_t[,c(ncol(x_t),2:ncol(x_t)-1)] # MOVE NEW COL TO FIRST
return(x_t)
}
major_test <- lapply(ERS_ID, XML_parser)
# major_test <- sapply(ERS_ID, XML_parser, simplify=FALSE)
# BIND DATA FRAMES TOGETHER
finaldf <- do.call(rbind, major_test)
# RESET ROW NAMES
row.names(finaldf) <- seq(nrow(finaldf))
答案 1 :(得分:1)
使用# in your model
def start_date
self[:start_date].strftime("%D %m %Y")
end
和xml2
您可以执行以下操作:
tidyverse
这为您提供了2x36 data.frame。要解析列类型,我建议使用require(xml2)
require(purrr)
require(tidyr)
urls <- rep("http://www.ebi.ac.uk/ena/data/view/ERS445758&display=xml", 2)
identifier <- LETTERS[seq_along(urls)] # Take a unique identifier per url here
parse_attribute <- function(x){
out <- data.frame(tag = xml_text(xml_find_all(x, "./TAG")),
value = xml_text(xml_find_all(x, "./VALUE")), stringsAsFactors = FALSE)
spread(out, tag, value)
}
doc <- map(urls, read_xml)
out <- doc %>%
map(xml_find_all, "//SAMPLE_ATTRIBUTE") %>%
set_names(identifier) %>%
map_df(parse_attribute, .id="url")
Out看起来如下:
readr::type_convert(out)
答案 2 :(得分:1)
purrr
在这里非常有用,因为您可以使用map
或使用at_depth
的嵌套元素迭代URL向量或XML文件列表,并简化结果使用*_df
表单和flatten
。
library(tidyverse)
library(xml2)
# be kind, don't call this more times than you need to
x <- c("ERS445758","ERS445759", "ERS445760", "ERS445761", "ERS445762") %>%
sprintf("http://www.ebi.ac.uk/ena/data/view/%s&display=xml", .) %>%
map(read_xml) # read each URL into a list item
df <- x %>% map(xml_find_all, '//SAMPLE_ATTRIBUTE') %>% # for each item select nodes
at_depth(2, as_list) %>% # convert each (nested) attribute to list
map_df(map_df, flatten) # flatten items, collect pages to df, then all to one df
df
## # A tibble: 175 × 3
## TAG VALUE UNITS
## <chr> <chr> <chr>
## 1 investigation type metagenome <NA>
## 2 project name BMRP <NA>
## 3 experimental factor microbiome <NA>
## 4 target gene 16S rRNA <NA>
## 5 target subfragment V1V2 <NA>
## 6 pcr primers 27F-338R <NA>
## 7 multiplex identifiers TGATACGTCT <NA>
## 8 sequencing method pyrosequencing <NA>
## 9 sequence quality check software <NA>
## 10 chimera check ChimeraSlayer; Usearch 4.1 database <NA>
## # ... with 165 more rows
答案 3 :(得分:0)
您可以使用逗号分隔的列表或范围(如ERS445758-ERS445762)使用单个REST网址retrieve multiple IDs,并避免对ENA进行多次查询。
此代码将所有5个样本放入一个节点集,然后使用xpath字符串中的前导点应用函数,使其相对于该节点。
ERS_ID <- c("ERS445758","ERS445759", "ERS445760", "ERS445761", "ERS445762")
url <- paste0( "http://www.ebi.ac.uk/ena/data/view/", paste(ERS_ID, collapse=","), "&display=xml")
doc <- xmlParse(url)
samples <- getNodeSet( doc, "//SAMPLE")
## check the first node
samples[[1]]
## get the sample attribute node set and apply xmlToDataFrame to that
x <- lapply( lapply(samples, getNodeSet, ".//SAMPLE_ATTRIBUTE"), xmlToDataFrame)
# labels for bind_rows
names(x) <- sapply(samples, xpathSApply, ".//PRIMARY_ID", xmlValue)
library(dplyr)
y <- bind_rows(x, .id="sample")
z <- subset(y, TAG %in% c("age","sex","body site","body-mass index") , 1:3)
sample TAG VALUE
15 ERS445758 age 28
16 ERS445758 sex male
17 ERS445758 body site Sigmoid colon
19 ERS445758 body-mass index 16.9550173
50 ERS445759 age 58
51 ERS445759 sex male
...
library(tidyr)
z %>% spread( TAG, VALUE)
sample age body site body-mass index sex
1 ERS445758 28 Sigmoid colon 16.9550173 male
2 ERS445759 58 Sigmoid colon 23.22543185 male
3 ERS445760 26 Sigmoid colon 20.76124567 female
4 ERS445761 30 Sigmoid colon 0 male
5 ERS445762 36 Sigmoid colon 0 male