Last updated: 2020-05-24

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Download Data - Online

To use data readily online. You need the readr package which reads csv files.

url <- "https://raw.githubusercontent.com/rafalab/dslabs/master/inst/extdata/murders.csv"
dat <- read_csv(url)

To download the file we can use: (or an alternative is to simply write.excel or write.csv).

download.file(url, tmp_filename)

Web Scrapping

If there isnt a csv/excel file to download, we can still access the data online and convert it into a dataframe. This is done from the rvest package, but is inbuilt in tidyverse. First, save the url page into an object in R url.

url <- "https://en.wikipedia.org/wiki/Murder_in_the_United_States_by_state"
h <- read_html(url)

If the HTML pages are divided into tables, you can extract it:

tab <- h %>% 
  html_nodes("table")
tab <- tab[[2]] #selecting the second node: which has the data.

tab <- tab %>% 
  html_table #finally a data with columns and rows

Set up coloumns names (makes sure it aligns with the data):

tab <- tab %>% 
  setNames(c("state", "population", "total", "murders", "gun_murders", "gun_ownership", "total_rate", "murder_rate", "gun_murder_rate"))
tab.data <- data.frame(tab) #data frame you can work with

Data from PDF

Sometimes important data are only in the form of a PDF. We can still use R to extract data from this. This is the test pdf page we use - link. We need the package pdftools.

temp_file <- tempfile() #code to create a unique name.
url <- "http://www.pnas.org/content/suppl/2015/09/16/1510159112.DCSupplemental/pnas.201510159SI.pdf" #url from which to download the table
download.file(url, temp_file) #downloading the file and giving it a temp name
txt <- pdf_text(temp_file) #converting the url into text value in R
file.remove(temp_file)

Now we look closely into the txt file to isolate our table. It is all about finding a pattern to isolate from.

raw.data <- txt[2] #our table was in the 2nd text.
raw.data1 <- str_split(raw.data, "\n") #each line in the table was seperated by "\n"
raw.data2 <- raw.data1[[1]] #isolating the section we need

table.1 <- raw.data2[3]
table.2 <- raw.data2[4]

Focusing on table.1 (column names)

table.1 <- table.1 %>%
  str_trim() %>%
  str_replace_all(",\\s.", "") %>%
  str_split("\\s{2,}", simplify = TRUE)
table.1 #we have the column names
     [,1]           [,2]     [,3]           
[1,] "Applications" "Awards" "Success rates"

Focusing on table.2 (more columns)

table.2 <- table.2 %>%
  str_trim() %>%
  str_split("\\s+", simplify = TRUE)
table.2
     [,1]         [,2]    [,3]  [,4]    [,5]    [,6]  [,7]    [,8]    [,9] 
[1,] "Discipline" "Total" "Men" "Women" "Total" "Men" "Women" "Total" "Men"
     [,10]  
[1,] "Women"

We can combine both these to form a column for our data:

tmp_names <- str_c(rep(table.1, each = 3), table.2[-1], sep = "_")
the_names <- c(table.2[1], tmp_names) %>%
  str_to_lower() %>%
  str_replace_all("\\s", "_")
the_names
 [1] "discipline"          "applications_total"  "applications_men"   
 [4] "applications_women"  "awards_total"        "awards_men"         
 [7] "awards_women"        "success_rates_total" "success_rates_men"  
[10] "success_rates_women"

Finally combining all this with the data:

new_research_funding_rates <- raw.data2[6:14] %>%
  str_trim %>%
  str_split("\\s{2,}", simplify = TRUE) %>%
  data.frame(stringsAsFactors = FALSE) %>%
  setNames(the_names) %>%
  mutate_at(-1, parse_number) #this is a new data.frame!

Removing Commas

Creating example data frame. Columns with commas are always chracter.

comma <- data.frame(c("1,233", "1,000,000"), c(1233, 1000000))
names(comma) <- c("Incorrect", "Correct")
comma
  Incorrect Correct
1     1,233    1233
2 1,000,000 1000000

parse_number is a direct function that deals with commas. There are more parse functions.

comma$Incorrect <- parse_number(comma$Incorrect)
comma
  Incorrect Correct
1      1233    1233
2   1000000 1000000

Numeric / Character

If x is character and y is numeric, and you want to reverse both these:

y <- as.numeric(x)
x <- as.character(y)

Wide / Long

This is mainly used to change WorldBank datasets. Example table:

# A tibble: 3 x 4
  Country `2001` `2002` `2003`
  <chr>    <dbl>  <dbl>  <dbl>
1 Nepal       12    435   5524
2 India       31    355   2424
3 China       64    353   2244

key The columns to turn into rows. value what to call the data.

long <- wide %>% 
  gather(key="Year", value="Population", 2:4)
long
# A tibble: 9 x 3
  Country Year  Population
  <chr>   <chr>      <dbl>
1 Nepal   2001          12
2 India   2001          31
3 China   2001          64
4 Nepal   2002         435
5 India   2002         355
6 China   2002         353
7 Nepal   2003        5524
8 India   2003        2424
9 China   2003        2244

Column Name

names(data)[1] <- "New_name"

NA’s

Counting NA’s in a Column

sum(is.na(tab.data$murders))


sessionInfo()
R version 4.0.0 (2020-04-24)
Platform: x86_64-apple-darwin17.0 (64-bit)
Running under: macOS Catalina 10.15.4

Matrix products: default
BLAS:   /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libRblas.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] pdftools_2.3.1  rvest_0.3.5     xml2_1.3.2      readxl_1.3.1   
 [5] forcats_0.5.0   stringr_1.4.0   dplyr_0.8.5     purrr_0.3.4    
 [9] readr_1.3.1     tidyr_1.0.3     tibble_3.0.1    ggplot2_3.3.0  
[13] tidyverse_1.3.0 workflowr_1.6.2

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.4.6     lubridate_1.7.8  lattice_0.20-41  assertthat_0.2.1
 [5] rprojroot_1.3-2  digest_0.6.25    utf8_1.1.4       R6_2.4.1        
 [9] cellranger_1.1.0 backports_1.1.6  reprex_0.3.0     evaluate_0.14   
[13] httr_1.4.1       pillar_1.4.4     rlang_0.4.6      curl_4.3        
[17] rstudioapi_0.11  whisker_0.4      rmarkdown_2.1    qpdf_1.1        
[21] selectr_0.4-2    munsell_0.5.0    broom_0.5.6      compiler_4.0.0  
[25] httpuv_1.5.2     modelr_0.1.7     xfun_0.13        pkgconfig_2.0.3 
[29] askpass_1.1      htmltools_0.4.0  tidyselect_1.1.0 fansi_0.4.1     
[33] crayon_1.3.4     dbplyr_1.4.3     withr_2.2.0      later_1.0.0     
[37] grid_4.0.0       nlme_3.1-147     jsonlite_1.6.1   gtable_0.3.0    
[41] lifecycle_0.2.0  DBI_1.1.0        git2r_0.27.1     magrittr_1.5    
[45] scales_1.1.1     cli_2.0.2        stringi_1.4.6    fs_1.4.1        
[49] promises_1.1.0   ellipsis_0.3.0   generics_0.0.2   vctrs_0.3.0     
[53] tools_4.0.0      glue_1.4.1       hms_0.5.3        yaml_2.2.1      
[57] colorspace_1.4-1 knitr_1.28       haven_2.2.0