允许用户选择要分析的数据文件的范围？

Question

我有以下XML文件：

<Company > 
    <shareprice> 
     <timeStamp> 12:00:00.01</timeStamp> 
     <Price> 25.02</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:00.02</timeStamp> 
     <Price> 15</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:01.025</timeStamp> 
     <Price> 15.02</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:01.031</timeStamp> 
     <Price> 18.25</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:01.039</timeStamp> 
     <Price> 18.54</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:01.050</timeStamp> 
     <Price> 16.52</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:02.01</timeStamp> 
     <Price> 17.50</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:03.01</timeStamp> 
     <Price> 25.02</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:05.02</timeStamp> 
     <Price> 30</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:11.025</timeStamp> 
     <Price> 32.25</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:12.031</timeStamp> 
     <Price> 26.05</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:15.039</timeStamp> 
     <Price> 18.54</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:19.050</timeStamp> 
     <Price> 16.52</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:01:02.01</timeStamp> 
     <Price> 17.50</Price> 
    </shareprice> 
</Company> 

而且我也有下列R-代码：

library (ggplot2) 
library (XML) 
df <- xmlToDataFrame(file.choose()) 
df$timeStamp <- strptime(as.character(df$timeStamp), "%H:%M:%OS") 
df$Price <- as.numeric(as.character(df$Price)) 
sapply(df, class)   
options("digits.secs"=3) 
summary (df)    
df$timeStamp <- df[1,"timeStamp"] + cumsum(runif(1:length(df$timeStamp))*60) 
summary(df) 
diff1 = 0 
diff <- append(diff1,diff(df$Price)) 
summary (df$Price) 
Ymin <- min(df$Price) 
Ymax <- max(df$Price) 
Ymedian <- median (df$Price) 
Ymean <- mean(df$Price) 
Ysd <- sd (df$Price) 
sink (file="c:/xampp/htdocs/Sharedata.xml", type="output",split=FALSE) 
cat("<graph caption=\"Share Data Wave\" subcaption=\"For Person's Name\" xAxisName=\"Time\" yAxisMinValue=\"-0.025\" yAxisName=\"Voltage\" decimalPrecision=\"5\" formatNumberScale=\"0\" numberPrefix=\"\" showNames=\"1\" showValues=\"0\" showAlternateHGridColor=\"1\" AlternateHGridColor=\"ff5904\" divLineColor=\"ff5904\" divLineAlpha=\"20\" alternateHGridAlpha=\"5\">\n") 
cat(sprintf(" <set name=\"%s\" value=\"%f\" hoverText = \"The difference from last value: %s\" ></set>\n", df$timeStamp, df$Price, diff)) 
cat ("</graph>\n") 
unlink("data.xml") 
sink (file="c:/xampp/htdocs/Sharesstatistics.xml", type="output",split=FALSE) 
cat (" <statistics>\n") 
cat (sprintf(" <mean>%s</mean>\n", Ymean)) 
cat (sprintf(" <sd>%s</sd>\n",Ysd)) 
cat (sprintf(" <min>%s</min>\n", Ymin)) 
cat (sprintf(" <median>%s</median>\n",Ymedian)) 
cat (sprintf(" <max>%s</max>\n", Ymax)) 
cat (" </statistics>\n") 
unlink("statistics.xml") 
quit() 

将R代码做所有我想要和需要它的完整的文件做。我的问题涉及如何让用户选择一个输入文件的范围来分析而不是完整的文件，这将如何完成？例如，如果用户只需要输入xml文件的第2到第5个输入并保持cat语句所定义的输出相同的输出。

<shareprice> 
     <timeStamp> 12:00:00.02</timeStamp> 
     <Price> 15</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:01.025</timeStamp> 
     <Price> 15.02</Price> 
    </shareprice> 

    <shareprice> 
     <timeStamp> 12:00:01.031</timeStamp> 
     <Price> 18.25</Price> 
    </shareprice> 

所有帮助非常感谢。

Regards，

Anthony。

Answer 1

这个问题很容易解决，只需读取数据框，然后要求用户使用例如扫描（n = 2）给出较低的记录上限。另请参阅？扫描。它允许您以交互方式提供输入，以便用户可以选择要执行的操作。这是输入要使用的数据范围的情况。

x <- scan(n=2) 
id <- min(x):max(x) 

df2 <- df[id,] 

如果您只想从非常大的XML表中读取必填字段，那就是另一回事了。我想不出一个内置函数来做到这一点，所以你将不得不做一些事情：

# function reads a subset of an xml file, 
# assuming a white line is dividing the individual records. 
# n is a vector containing the record numbers wanted 

subset.xml <- function(x,n,...){ 
    # set a range if n is just a number 
    if (length(n)==1) n <- 1:n 

    #initiate vars 
    skp <- 0 # the number of lines to skip by scan 
    count <- 1 
    out <- character(1) 

    repeat{ 
     tmp <- scan(x,what=character(0),n=1,skip=skp,blank.lines.skip=F,sep="\n") 
     skp <- skp+1 
     if(length(tmp)==0) {break} # no more input 

     if((count %in% n) & (tmp !="")) out <- paste(out,tmp,sep="\n") 
     if(tmp=="") count <- count+1 # white line seperates records 
    } 
    out <- substring(out,3) 
    out <- paste("<Data>",out,"</Data>",sep="\n") 
    return(xmlToDataFrame(xmlParse(out))) 
} 

df <- subset.xml("test.xml",2:4) 
> df 
     timeStamp Price 
1 12:00:00.02  15 
2 12:00:01.025 15.02 
3 12:00:01.031 18.25