How to parse XML to R data frame

Question

I tried to parse XML to R data frame  this link helped me a lot   how to create an R data frame from a xml file  But still I was not able to figure out my problem   Here is my code   data  lt - xmlParse  http   forecast weather gov MapClick php lat 29 803 amp lon -82 411 amp FcstType digitalDWML   xmlToDataFrame nodes getNodeSet data1    data    c  location   time-layout    step1  lt - xmlToDataFrame nodes getNodeSet data1    location point    c  latitude   longitude    step2  lt - xmlToDataFrame nodes getNodeSet data1    time-layout start-valid-time    step3  lt - xmlToDataFrame nodes getNodeSet data1    parameters temperature    c  type  hourly       The data frame I want to have is like this   latitude  longitude   start-valid-time   hourly temperature 29 803     -82 411  2013-06-19T15 00 00-04 00    91 29 803     -82 411  2013-06-19T16 00 00-04 00    90   I m stuck at the xmlToDataFrame    Any help would be very much appreciated  thanks

User · Answer

Here s a partial solution using xml2  Breaking the solution up into smaller pieces generally makes it easier to ensure everything is lined up   library xml2  data  lt - read xml  http   forecast weather gov MapClick php lat 29 803 amp lon -82 411 amp FcstType digitalDWML      Point locations point  lt - data   gt   xml find all    point   point   gt   xml attr  latitude     gt   as numeric   point   gt   xml attr  longitude     gt   as numeric      Start time data   gt      xml find all    start-valid-time     gt      xml text      Temperature data   gt      xml find all    temperature  type  hourly   value     gt      xml text     gt      as integer

User · Answer

You can try the code below     Load the packages required to read XML files  library  XML   library  methods      Convert the input xml file to a data frame  xmldataframe  lt - xmlToDataFrame  input xml   print xmldataframe

User · Answer

Use xpath more directly for both performance and clarity   time path  lt -    start-valid-time  temp path  lt -    temperature  type  hourly   value   df  lt - data frame      latitude data   number   point  latitude          longitude data   number   point  longitude          start valid time sapply data time path   xmlValue       hourly temperature as integer sapply data temp path   as   integer      leading to   gt  head df  2    latitude longitude          start valid time hourly temperature 1    29 81    -82 42 2014-02-14T18 00 00-05 00                 60 2    29 81    -82 42 2014-02-14T19 00 00-05 00                 55

User · Answer

Data in XML format are rarely organized in a way that would allow the xmlToDataFrame function to work  You re better off extracting everything in lists and then binding the lists together in a data frame   require XML  data  lt - xmlParse  http   forecast weather gov MapClick php lat 29 803 amp lon -82 411 amp FcstType digitalDWML    xml data  lt - xmlToList data    In the case of your example data  getting location and start time is fairly straightforward   location  lt - as list xml data   data      location      point      start time  lt - unlist xml data   data      time-layout         names xml data   data      time-layout         start-valid-time      Temperature data is a bit more complicated  First you need to get to the node that contains the temperature lists  Then you need extract both the lists  look within each one  and pick the one that has  hourly  as one of its values  Then you need to select only that list but only keep the values that have the  value  label   temps  lt - xml data   data      parameters    temps  lt - temps names temps      temperature   temps  lt - temps sapply temps  function x  any unlist x      hourly     temps  lt - unlist temps  1   sapply temps  names      value     out  lt - data frame    as list location      start valid time    start time     hourly temperature    temps   head out    latitude longitude          start valid time hourly temperature 1    29 81    -82 42 2013-06-19T16 00 00-04 00                 91 2    29 81    -82 42 2013-06-19T17 00 00-04 00                 90 3    29 81    -82 42 2013-06-19T18 00 00-04 00                 89 4    29 81    -82 42 2013-06-19T19 00 00-04 00                 85 5    29 81    -82 42 2013-06-19T20 00 00-04 00                 83 6    29 81    -82 42 2013-06-19T21 00 00-04 00                 80

[xml] How to parse XML to R data frame

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