AccessWebData

1. Import all required libraries

# This package is required for Accessing APIS (HTTP or HTTPS URLS from Web)
library(httr)
#This package exposes some additional functions to convert json/text to data frame
library(rlist)
#This package exposes some additional functions to convert json/text to data frame
library(jsonlite)
#This library is used to manipulate data
library(dplyr)

## 
## Attaching package: 'dplyr'

## The following objects are masked from 'package:stats':
## 
##     filter, lag

## The following objects are masked from 'package:base':
## 
##     intersect, setdiff, setequal, union

resp<-GET("https://reqres.in/api/users?pageid=2")
#.When we get the response from API we will use to very basic methods of httr.
http_type(resp)  #. This method will tell us what is the type of response fetched from GET() call to the API.

## [1] "application/json"

http_error(resp) #. This method just verifies if the response is error free for processing

## [1] FALSE

query<-list(page="2")

resp<-GET("https://reqres.in/api/users",query=query)

http_type(resp)  

## [1] "application/json"

http_error(resp) 

## [1] FALSE

# Shows raw data which is not structured and readable
jsonRespText<-content(resp,as="text") 
jsonRespText

## [1] "{\"page\":2,\"per_page\":3,\"total\":12,\"total_pages\":4,\"data\":[{\"id\":4,\"first_name\":\"Eve\",\"last_name\":\"Holt\",\"avatar\":\"https://s3.amazonaws.com/uifaces/faces/twitter/marcoramires/128.jpg\"},{\"id\":5,\"first_name\":\"Charles\",\"last_name\":\"Morris\",\"avatar\":\"https://s3.amazonaws.com/uifaces/faces/twitter/stephenmoon/128.jpg\"},{\"id\":6,\"first_name\":\"Tracey\",\"last_name\":\"Ramos\",\"avatar\":\"https://s3.amazonaws.com/uifaces/faces/twitter/bigmancho/128.jpg\"}]}"

# Structurised data in form of R vectors and lists
jsonRespParsed<-content(resp,as="parsed") 
jsonRespParsed

## $page
## [1] 2
## 
## $per_page
## [1] 3
## 
## $total
## [1] 12
## 
## $total_pages
## [1] 4
## 
## $data
## $data[[1]]
## $data[[1]]$id
## [1] 4
## 
## $data[[1]]$first_name
## [1] "Eve"
## 
## $data[[1]]$last_name
## [1] "Holt"
## 
## $data[[1]]$avatar
## [1] "https://s3.amazonaws.com/uifaces/faces/twitter/marcoramires/128.jpg"
## 
## 
## $data[[2]]
## $data[[2]]$id
## [1] 5
## 
## $data[[2]]$first_name
## [1] "Charles"
## 
## $data[[2]]$last_name
## [1] "Morris"
## 
## $data[[2]]$avatar
## [1] "https://s3.amazonaws.com/uifaces/faces/twitter/stephenmoon/128.jpg"
## 
## 
## $data[[3]]
## $data[[3]]$id
## [1] 6
## 
## $data[[3]]$first_name
## [1] "Tracey"
## 
## $data[[3]]$last_name
## [1] "Ramos"
## 
## $data[[3]]$avatar
## [1] "https://s3.amazonaws.com/uifaces/faces/twitter/bigmancho/128.jpg"

fromJSON(jsonRespText)

## $page
## [1] 2
## 
## $per_page
## [1] 3
## 
## $total
## [1] 12
## 
## $total_pages
## [1] 4
## 
## $data
##   id first_name last_name
## 1  4        Eve      Holt
## 2  5    Charles    Morris
## 3  6     Tracey     Ramos
##                                                                avatar
## 1 https://s3.amazonaws.com/uifaces/faces/twitter/marcoramires/128.jpg
## 2  https://s3.amazonaws.com/uifaces/faces/twitter/stephenmoon/128.jpg
## 3    https://s3.amazonaws.com/uifaces/faces/twitter/bigmancho/128.jpg

modJson<-jsonRespParsed$data #. Access data element of whole list and ignore other vectors
modJson

## [[1]]
## [[1]]$id
## [1] 4
## 
## [[1]]$first_name
## [1] "Eve"
## 
## [[1]]$last_name
## [1] "Holt"
## 
## [[1]]$avatar
## [1] "https://s3.amazonaws.com/uifaces/faces/twitter/marcoramires/128.jpg"
## 
## 
## [[2]]
## [[2]]$id
## [1] 5
## 
## [[2]]$first_name
## [1] "Charles"
## 
## [[2]]$last_name
## [1] "Morris"
## 
## [[2]]$avatar
## [1] "https://s3.amazonaws.com/uifaces/faces/twitter/stephenmoon/128.jpg"
## 
## 
## [[3]]
## [[3]]$id
## [1] 6
## 
## [[3]]$first_name
## [1] "Tracey"
## 
## [[3]]$last_name
## [1] "Ramos"
## 
## [[3]]$avatar
## [1] "https://s3.amazonaws.com/uifaces/faces/twitter/bigmancho/128.jpg"

#Using dplyr and base R
modJson%>%bind_rows%>%select(id,first_name,last_name,avatar)

## # A tibble: 3 x 4
##      id first_name last_name avatar                                       
##   <int> <chr>      <chr>     <chr>                                        
## 1     4 Eve        Holt      https://s3.amazonaws.com/uifaces/faces/twitt~
## 2     5 Charles    Morris    https://s3.amazonaws.com/uifaces/faces/twitt~
## 3     6 Tracey     Ramos     https://s3.amazonaws.com/uifaces/faces/twitt~

list.select(modJson,id,first_name)

## [[1]]
## [[1]]$id
## [1] 4
## 
## [[1]]$first_name
## [1] "Eve"
## 
## 
## [[2]]
## [[2]]$id
## [1] 5
## 
## [[2]]$first_name
## [1] "Charles"
## 
## 
## [[3]]
## [[3]]$id
## [1] 6
## 
## [[3]]$first_name
## [1] "Tracey"

list.stack(modJson)

##   id first_name last_name
## 1  4        Eve      Holt
## 2  5    Charles    Morris
## 3  6     Tracey     Ramos
##                                                                avatar
## 1 https://s3.amazonaws.com/uifaces/faces/twitter/marcoramires/128.jpg
## 2  https://s3.amazonaws.com/uifaces/faces/twitter/stephenmoon/128.jpg
## 3    https://s3.amazonaws.com/uifaces/faces/twitter/bigmancho/128.jpg

1. Results obtained from dplyr and baseR and with rlist pacakges are ver similar.

post_result <- POST(url="http://httpbin.org/post",body="this is a test") # where body argument accpets data we wish to send to server