607 Week 4 Assignment

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• 3. Copy the introductory example. The vector name stores the extracted names.

     R> name
     [1] "Moe Szyslak" "Burns, C. Montgomery" "Rev. Timothy Lovejoy"
     [4] "Ned Flanders" "Simpson, Homer" "Dr. Julius Hibbert"
     

  • 1. Use the tools of this chapter to rearrange the vector so that all elements conform to the standard first_name last_name.

    Below is what we have

    library(stringr)
    raw.data <- "555-1239Moe Szyslak(636) 555-0113Burns, C. Montgomery555
    -6542Rev. Timothy Lovejoy555 8904Ned Flanders636-555-3226Simpson, Homer5553642Dr. Julius Hibbert"
    
    name <- unlist(str_extract_all(raw.data, "[[:alpha:]., ]{2,}"))
    name

    ## [1] "Moe Szyslak"          "Burns, C. Montgomery" "Rev. Timothy Lovejoy"
    ## [4] "Ned Flanders"         "Simpson, Homer"       "Dr. Julius Hibbert"

    • To get standard names below are steps

      1. we need to convert list to dataframe
      2. rename it

      #convert list to dataframe
      namesdf<-do.call(rbind, lapply(name, data.frame, stringsAsFactors=FALSE))
      #rename column
      namesdf$names<-namesdf$X..i..

      3. If name contains comma, that means last name is first and first name is last.so re-arrange it

      namesdf$stdFormatNames<-ifelse(grepl( ",",namesdf$names),paste(word(namesdf$names,-1),word(namesdf$names,1)),namesdf$names)

      4. remove prefixes and commas

      namesdf$stdFormatNames<-gsub("Rev.|Dr.|,","", namesdf$stdFormatNames)
      namesdf$stdFormatNames

      ## [1] "Moe Szyslak"      "Montgomery Burns" " Timothy Lovejoy"
      ## [4] "Ned Flanders"     "Homer Simpson"    " Julius Hibbert"

  • 2. Construct a logical vector indicating whether a character has a title (i.e., Rev. and Dr.).

  • Using str_detect to check if there is title in name

    namesdf$names

    ## [1] "Moe Szyslak"          "Burns, C. Montgomery" "Rev. Timothy Lovejoy"
    ## [4] "Ned Flanders"         "Simpson, Homer"       "Dr. Julius Hibbert"

    namesdf$hasTitle<-str_detect(namesdf$names, "Rev.|Dr.")
    namesdf$names

    ## [1] "Moe Szyslak"          "Burns, C. Montgomery" "Rev. Timothy Lovejoy"
    ## [4] "Ned Flanders"         "Simpson, Homer"       "Dr. Julius Hibbert"

    namesdf[,c("names","hasTitle")]

    ##                  names hasTitle
    ## 1          Moe Szyslak    FALSE
    ## 2 Burns, C. Montgomery    FALSE
    ## 3 Rev. Timothy Lovejoy     TRUE
    ## 4         Ned Flanders    FALSE
    ## 5       Simpson, Homer    FALSE
    ## 6   Dr. Julius Hibbert     TRUE

  • 3. Construct a logical vector indicating whether a character has a second name.

  • Spliting by space

    namesdf$stdFormatNames

    ## [1] "Moe Szyslak"      "Montgomery Burns" " Timothy Lovejoy"
    ## [4] "Ned Flanders"     "Homer Simpson"    " Julius Hibbert"

    grepl( " ",str_trim(namesdf$stdFormatNames))

    ## [1] TRUE TRUE TRUE TRUE TRUE TRUE

• 7. Consider the string . We would like to extract the first HTML tag. To do so we write the regular expression <.+>. Explain why this fails and correct the expression.

  • R applies greedy quantification. This means that the program tries to extract the greatest possible sequence of the preceding character. As the . matches any character, the function returns the greatest possible sequence of any characters before a sequence of sentence.

    stringToSearch<-"<title>+++BREAKING NEWS+++</title>"
    str_extract(stringToSearch,"<.+>")

    ## [1] "<title>+++BREAKING NEWS+++</title>"

    We can change this behavior by adding a ? to the expression in order to signal that we are only looking for the shortest possible sequence of any characters before a sequence of sentence.

    str_extract(stringToSearch, "<.+?>")

    ## [1] "<title>"

• 8. Consider the string (5-3)²⁼⁵2-253+3^2 conforms to the binomial theorem. We would like to extract the formula in the string. To do so we write the regular expression [^0-9=+*()]+. Explain why this fails and correct the expression.

  • Putting the caret at the beginning of a character class does the inverse. keeping it at the end resolves the problem.

    binomial_str <- "(5-3)^2=5^2-2*5*3+3^2 conforms to the binomial theorem."
    str_extract(binomial_str, "[^0-9=+*()]+")

    ## [1] "-"

    str_extract(binomial_str, "[0-9=+*()^-]+")

    ## [1] "(5-3)^2=5^2-2*5*3+3^2"