Parsing xml data with R. The code is very slow. How to make it faster?

Question

I have a very big dataset (about 20 GB) in xml format and I need to parse it into tidy tables to make some statistics. I want to save:
- attribute tag for tag controlfield
- attribute tag for tag datafield
- attribute code for tag subfield
- values that correspond to all these attributes/tags

Folowing example from here (R XML - combining parent and child nodes into data frame) I wrote my own script. It works correctly but it is very very slow... I have more than 1 million records so the script is not practical but I don't know how to optimize it.
Is there a way to improve the performance of my code or is there another way to solve the problem. For me it is not important what package to use (xml2 or xml or some other). What I really need is to convert my data into tidy tables as fast as possible. Here is my data, some comments to data and the code.

Thank you for all possible help.

Data

library(xml2)
library(tidyverse)
df <- read_xml(
'<collection>
<record>
  <controlfield tag="001">1</controlfield>
  <controlfield tag="005">20180109004353.0</controlfield>
  <datafield tag="020" ind1=" " ind2=" ">
    <subfield code="a">9780821812419</subfield>
    <subfield code="b">print</subfield>
  </datafield>
  <datafield tag="020" ind1=" " ind2=" ">
    <subfield code="a">9780821899854</subfield>
    <subfield code="b">online</subfield>
  </datafield>
  <datafield tag="024" ind1="7" ind2=" ">
    <subfield code="2">DOI</subfield>
    <subfield code="a">10.1090/memo/0041</subfield>
  </datafield>
  <datafield tag="035" ind1=" " ind2=" ">
    <subfield code="9">SPIRESTeX</subfield>
    <subfield code="a">Wong:1961af</subfield>
  </datafield>
  <datafield tag="035" ind1=" " ind2=" ">
    <subfield code="9">MSNET</subfield>
    <subfield code="a">0383311</subfield>
  </datafield>
  <datafield tag="035" ind1=" " ind2=" ">
    <subfield code="9">ZBLATT</subfield>
    <subfield code="a">0124.13401</subfield>
  </datafield>
  <datafield tag="650" ind1="1" ind2="7">
    <subfield code="2">INSPIRE</subfield>
    <subfield code="a">Math and Math Physics</subfield>
  </datafield>
  <datafield tag="773" ind1=" " ind2=" ">
    <subfield code="c">1-112</subfield>
    <subfield code="p">Mem.Am.Math.Soc.</subfield>
    <subfield code="v">41</subfield>
    <subfield code="y">1961</subfield>
    <subfield code="1">1214590</subfield>
  </datafield>
  <datafield tag="970" ind1=" " ind2=" ">
    <subfield code="a">SPIRES-60</subfield>
  </datafield>
  <datafield tag="980" ind1=" " ind2=" ">
    <subfield code="a">Book</subfield>
  </datafield>
  <datafield tag="980" ind1=" " ind2=" ">
    <subfield code="a">Citeable</subfield>
  </datafield>
  <datafield tag="980" ind1=" " ind2=" ">
    <subfield code="a">HEP</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">1</subfield>
    <subfield code="s">Ann.Math.,43,161</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">2</subfield>
    <subfield code="s">Am.Math.Mon.,53,136</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="h">E. Cartan</subfield>
    <subfield code="m">Paris</subfield>
    <subfield code="o">3</subfield>
    <subfield code="t">Lecons sur la theorie des spineurs I</subfield>
    <subfield code="y">1938</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">4</subfield>
    <subfield code="s">Enseign.Math.,40,26</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="s">Annals Math.,47,510</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">6</subfield>
    <subfield code="s">Comment.Math.Helv.,15,358</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">9</subfield>
    <subfield code="s">Trans.Am.Math.Soc.,61,193</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">10</subfield>
    <subfield code="s">Math.Ann.,88,1</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">12</subfield>
    <subfield code="s">Math.Ann.,60,546</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">14</subfield>
    <subfield code="s">Comment.Math.Helv.,21,261</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">17</subfield>
    <subfield code="s">Abh.Math.Sem.Univ.Hamburg,1,1</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">18</subfield>
    <subfield code="s">Am.J.Math.,67,472</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">20</subfield>
    <subfield code="s">Comment.Math.Helv.,8,3</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="9">CURATOR</subfield>
    <subfield code="o">21</subfield>
    <subfield code="s">Tohoku Math.J.,3,322</subfield>
  </datafield>
  <datafield tag="909" ind1="C" ind2="O">
    <subfield code="o">oai:inspirehep.net:1</subfield>
    <subfield code="p">INSPIRE:HEP</subfield>
  </datafield>
  <datafield tag="961" ind1=" " ind2=" ">
    <subfield code="x">2001-02-23</subfield>
    <subfield code="c">2018-01-09</subfield>
  </datafield>
  <datafield tag="245" ind1=" " ind2=" ">
    <subfield code="a">Isoclinic N planes in Euclidean 2N space, Clifford parallels in elliptic (2N-1) space, and the Hurwitz matrix equations</subfield>
  </datafield>
  <datafield tag="246" ind1=" " ind2=" ">
    <subfield code="9">arXiv</subfield>
    <subfield code="a">Isoclinic n-planes in Euclidean 2n-space, Clifford parallels in elliptic (2n-1)-space, and the Hurwitz matrix equations</subfield>
  </datafield>
  <datafield tag="100" ind1=" " ind2=" ">
    <subfield code="a">Wong, Yung-Chow</subfield>
    <subfield code="u">Hong Kong U.</subfield>
    <subfield code="w">Y.C.Wong.1</subfield>
    <subfield code="y">0</subfield>
    <subfield code="z">908370</subfield>
  </datafield>
  <datafield tag="269" ind1=" " ind2=" ">
    <subfield code="c">1961</subfield>
  </datafield>
  <datafield tag="300" ind1=" " ind2=" ">
    <subfield code="a">121</subfield>
  </datafield>
  <datafield tag="500" ind1=" " ind2=" ">
    <subfield code="a">Second printing with corrections 1971 (ISBN: 0-8218-1241-6).</subfield>
  </datafield>
  <datafield tag="520" ind1=" " ind2=" ">
    <subfield code="a">Introduction Part I. Isoclinic nn-planes in E2nE2n and Clifford parallel</subfield>
  </datafield>
</record>

<record>
  <controlfield tag="001">17</controlfield>
  <controlfield tag="005">20190325225547.0</controlfield>
  <datafield tag="035" ind1=" " ind2=" ">
    <subfield code="9">SPIRESTeX</subfield>
    <subfield code="a">Breymayer:1963bh</subfield>
  </datafield>
  <datafield tag="037" ind1=" " ind2=" ">
    <subfield code="a">SLAC-TN-63-023</subfield>
  </datafield>
  <datafield tag="100" ind1=" " ind2=" ">
    <subfield code="a">Breymayer, K.E.</subfield>
    <subfield code="u">SLAC</subfield>
    <subfield code="w">K.E.Breymayer.1</subfield>
    <subfield code="y">0</subfield>
    <subfield code="z">903206</subfield>
  </datafield>
  <datafield tag="245" ind1=" " ind2=" ">
    <subfield code="a">SYSTEM INTERCONNECTION AND PROTECTION OF THE MODULATOR</subfield>
  </datafield>
  <datafield tag="269" ind1=" " ind2=" ">
    <subfield code="c">1963-03</subfield>
  </datafield>
  <datafield tag="300" ind1=" " ind2=" ">
    <subfield code="a">21</subfield>
  </datafield>
  <datafield tag="650" ind1="1" ind2="7">
    <subfield code="2">INSPIRE</subfield>
  </datafield>
  <datafield tag="700" ind1=" " ind2=" ">
    <subfield code="a">Mallory, Kenneth B.</subfield>
    <subfield code="u">SLAC</subfield>
    <subfield code="w">K.B.Mallory.1</subfield>
    <subfield code="y">0</subfield>
    <subfield code="z">903206</subfield>
  </datafield>
  <datafield tag="710" ind1=" " ind2=" ">
    <subfield code="a">SLAC</subfield>
  </datafield>
  <datafield tag="856" ind1="4" ind2=" ">
    <subfield code="u">http://www-public.slac.stanford.edu/sciDoc/docMeta.aspx?slacPubNumber=slac-tn-63-023</subfield>
    <subfield code="w">slac-tn-63-023</subfield>
    <subfield code="y">SLAC</subfield>
  </datafield>
  <datafield tag="856" ind1="4" ind2=" ">
    <subfield code="s">1903536</subfield>
    <subfield code="u">http://inspirehep.net/record/17/files/slac-tn-63-023.pdf</subfield>
  </datafield>
  <datafield tag="909" ind1="C" ind2="O">
    <subfield code="o">oai:inspirehep.net:17</subfield>
    <subfield code="p">INSPIRE:HEP</subfield>
  </datafield>
  <datafield tag="961" ind1=" " ind2=" ">
    <subfield code="x">1963-03-01</subfield>
    <subfield code="c">2019-03-25</subfield>
  </datafield>
  <datafield tag="970" ind1=" " ind2=" ">
    <subfield code="a">SPIRES-329</subfield>
  </datafield>
  <datafield tag="980" ind1=" " ind2=" ">
    <subfield code="a">HEP</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="6">
    <subfield code="a">0-0-0-0-0-0-1</subfield>
    <subfield code="t">2014-08-13 15:34:53</subfield>
    <subfield code="v">Invenio/1.1.2.1260-aa76f refextract/1.5.44</subfield>
    <subfield code="v">content.pdf;1</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="m">will open, thus o~nlng the ac cQxuit to the -</subfield>
    <subfield code="o">1</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="m">2</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="m">Apply the trigger. If the high voltage is present, the klystron is pulsed and draws average current</subfield>
    <subfield code="o">3</subfield>
    <subfield code="t">relay comes on. In addI.tion, a light at the modulator comes on, indicating Klystron Current</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="m">no recycling</subfield>
    <subfield code="o">3</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="m">removes the 260-6~0 vous l (2) Resetting: close circuit breaker only, no further action necessary if fault is cleared.</subfield>
    <subfield code="o">3</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="m">% u --L--_ I ‘2 Q-4 -r---.‘-i-’I ___----_.--_.-_. -.L.-</subfield>
    <subfield code="o">4</subfield>
  </datafield>
</record>

<record>
  <controlfield tag="001">18</controlfield>
  <controlfield tag="005">20140813111316.0</controlfield>
  <datafield tag="035" ind1=" " ind2=" ">
    <subfield code="a">Johnston:1977saa</subfield>
    <subfield code="9">INSPIRETeX</subfield>
  </datafield>
  <datafield tag="037" ind1=" " ind2=" ">
    <subfield code="a">SLAC-PUB-0341</subfield>
  </datafield>
  <datafield tag="100" ind1=" " ind2=" ">
    <subfield code="a">Johnston, Lawrence II.</subfield>
    <subfield code="u">SLAC</subfield>
    <subfield code="w">L.H.Johnston.1</subfield>
    <subfield code="y">0</subfield>
    <subfield code="z">903206</subfield>
  </datafield>
  <datafield tag="245" ind1=" " ind2=" ">
    <subfield code="a">A target beam monitor using secondary electron emission</subfield>
  </datafield>
  <datafield tag="269" ind1=" " ind2=" ">
    <subfield code="c">1977-08</subfield>
  </datafield>
  <datafield tag="300" ind1=" " ind2=" ">
    <subfield code="a">17</subfield>
  </datafield>
  <datafield tag="700" ind1=" " ind2=" ">
    <subfield code="a">Murray, Joseph J.</subfield>
    <subfield code="u">SLAC</subfield>
    <subfield code="w">J.J.Murray.1</subfield>
    <subfield code="y">0</subfield>
    <subfield code="z">903206</subfield>
  </datafield>
  <datafield tag="700" ind1=" " ind2=" ">
    <subfield code="a">Gearhart, Roger A.</subfield>
    <subfield code="u">LBL, Berkeley</subfield>
    <subfield code="w">R.Gearhart.1</subfield>
    <subfield code="y">0</subfield>
    <subfield code="z">902953</subfield>
  </datafield>
  <datafield tag="700" ind1=" " ind2=" ">
    <subfield code="a">Hauser, Todd</subfield>
    <subfield code="u">LBL, Berkeley</subfield>
    <subfield code="w">T.Hauser.2</subfield>
    <subfield code="y">0</subfield>
    <subfield code="z">902953</subfield>
  </datafield>
  <datafield tag="700" ind1=" " ind2=" ">
    <subfield code="a">Klein, Paul R.</subfield>
    <subfield code="u">Purdue U.</subfield>
    <subfield code="w">P.Klein.2</subfield>
    <subfield code="y">0</subfield>
    <subfield code="z">903142</subfield>
  </datafield>
  <datafield tag="856" ind1="4" ind2=" ">
    <subfield code="w">0341</subfield>
    <subfield code="y">SLACPUB</subfield>
    <subfield code="u">http://www-public.slac.stanford.edu/sciDoc/docMeta.aspx?slacPubNumber=SLAC-PUB-0341</subfield>
  </datafield>
  <datafield tag="856" ind1="4" ind2=" ">
    <subfield code="s">1110230</subfield>
    <subfield code="u">http://inspirehep.net/record/18/files/slac-pub-0341.pdf</subfield>
  </datafield>
  <datafield tag="909" ind1="C" ind2="O">
    <subfield code="o">oai:inspirehep.net:18</subfield>
    <subfield code="p">INSPIRE:HEP</subfield>
  </datafield>
  <datafield tag="961" ind1=" " ind2=" ">
    <subfield code="x">1977-01-01</subfield>
    <subfield code="c">2014-08-13</subfield>
  </datafield>
  <datafield tag="970" ind1=" " ind2=" ">
    <subfield code="a">SPIRES-337</subfield>
  </datafield>
  <datafield tag="980" ind1=" " ind2=" ">
    <subfield code="a">HEP</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="s">Rev.Sci.Instrum.,26,229</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="s">IEEE Trans.Nucl.Sci.,12,935</subfield>
    <subfield code="0">48647</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="s">Nucl.Instrum.Meth.,15,63</subfield>
  </datafield>
  <datafield tag="999" ind1="C" ind2="5">
    <subfield code="s">Phys.Rev.Lett.,18,366</subfield>
  </datafield>
</record>
</collection>')

Comments to tags:
<controlfield tag="001">This is identifier of the record</controlfield>
<controlfield tag="005">This is time of last record update</controlfield>

My code

start_t <- Sys.time()
x1 <- df %>% xml_find_all('.//record')

x2 <- x1 %>% 
    xml_find_all('.//datafield') %>% 
    map_df(~list(rec      = list(map(xml_find_all(.x, './/preceding-sibling::controlfield'), xml_text)),
                 attrs    = list(xml_attr(.x, attr = 'tag')), 
                 variable = list(map(xml_children(.x), xml_attrs)), 
                 value    = list(map(xml_children(.x), xml_text))
                 ))

x2_tidy <- x2 %>% unnest(c(variable, value)) %>% mutate(rec = as.character(rec))
Sys.time() - start_t

Update My result is like this. Sorry, I can't figure out how to add text table here, so I add it like an image. Image with resulting table

What do you want the output to look like? Can you provide an example table structure? Your code doesn't work for me, but I have an approach, just need to be sure on same page — Carl Boneri, Oct 30 '19 at 08:31
Thank you very much for your answer. I added image with the result table. Sorry for this inconvenience. — StackQuestions, Oct 30 '19 at 09:05
In fact, as your can see in table, my column "rec" is list, converted to character. This is because, if I unlist it in my code, it works even more slowly. So I decided to leave it "as is" to correct it later and divide in to columns record identifier and edit time. That is in final result I want to have table with 5 columns: record_id, edit_time, attrs, variable, value. — StackQuestions, Oct 30 '19 at 09:13
when you say **variable**, do you mean the value of the attribute? — Carl Boneri, Oct 30 '19 at 09:23
Yes, these are values of attribute "code" like "a", "z", etc. — StackQuestions, Oct 30 '19 at 09:26
got it, so to be clear you dont care about the attributes in datafield like `ind1` or `ind2` — Carl Boneri, Oct 30 '19 at 09:42

Carl Boneri · Answer 1 · 2019-10-30T10:02:52.420

Okay, so just because i dove down the rabbit hole here... below is working code. I don't know why you would want to structure your output data this way, though, and just in case you later decide on another formatting, I included a col for the name of the node the record(line/row) is associated with not record node

Note i am using library(xml2) for all of this:

Here's a function to do the work on the attributes we need:

.attrs_targeted <- function(x){
  ats <- xml_attrs(x)
  ats_array <- unlist(ats)
  hits <- grepl("tag|code", names(ats_array), ignore.case = TRUE, perl = TRUE)
  ats <- ats_array[hits]
  data.frame(
    attrs = names(ats),
    variable = ats,
    row.names = NULL,
    stringsAsFactors = FALSE
  )
}

Here are the record nodes:

records <- xml_find_all(df, ".//record")
> records
{xml_nodeset (3)}
[1] <record>\n  <controlfield tag="001">1</controlfield>\n  <controlfield tag="005">20180109004353.0</controlfield>\n  <datafield tag="020" ind1=" " ind2=" ">\n    <subfield code="a">9780821812419</subfiel ...
[2] <record>\n  <controlfield tag="001">17</controlfield>\n  <controlfield tag="005">20190325225547.0</controlfield>\n  <datafield tag="035" ind1=" " ind2=" ">\n    <subfield code="9">SPIRESTeX</subfield>\ ...
[3] <record>\n  <controlfield tag="001">18</controlfield>\n  <controlfield tag="005">20140813111316.0</controlfield>\n  <datafield tag="035" ind1=" " ind2=" ">\n    <subfield code="a">Johnston:1977saa</sub ...
>

And here is our iterator:

library(dplyr)
library(jsonlite)

results <- rbind_pages(lapply(records, function(i){
  # Controlfield nodes
  controls <- xml_find_all(i, ".//controlfield")
  # control attributes
  ats <- .attrs_targeted(controls)
  # control values
  c_vals <- xml_text(controls)
  # store on a data frame
  d <- data.frame(
    node_name = xml_name(controls),
    record_id = c_vals[[1]], 
    edit_time = c_vals[[2]],
    ats, 
    value = c_vals
  )
  # now to the datafields
  dfields <- xml_find_all(i, ".//datafield")
  # loop through the datafield nodes, and then the subfield nodes, which have code/values we want, but build and 
  # bind data.frames along the way
  d_loop <- rbind_pages(lapply(dfields, function(j){
    d_ats <- .attrs_targeted(j)
    d2 <- data.frame(
      node_name = xml_name(j),
      d_ats,
      value = NA
    )
    # Now target the subfields
    sfields <- xml_find_all(j, ".//subfield")
    d3 <- rbind_pages(Map(function(k){
      data.frame(
        node_name = xml_name(k),
        .attrs_targeted(k),
        value = xml_text(k)
      )
    }, sfields))
    rbind_pages(list(d2, d3))
  })) %>% mutate(record_id = c_vals[[1]], edit_time = c_vals[[2]]) # add the records back in

  rbind_pages(list(d, d_loop))
}))

> head(results)
     node_name record_id        edit_time attrs variable            value
1 controlfield         1 20180109004353.0   tag      001                1
2 controlfield         1 20180109004353.0   tag      005 20180109004353.0
3    datafield         1 20180109004353.0   tag      020             <NA>
4     subfield         1 20180109004353.0  code        a    9780821812419
5     subfield         1 20180109004353.0  code        b            print
6    datafield         1 20180109004353.0   tag      020             <NA>

To peek in at the data:

 results %>% filter(attrs == "code") %>% data.table::dcast(record_id ~ variable)
  record_id 0 1 2  9  a b c h m  o p  s t u v w x y z
1         1 0 1 2 18 17 2 3 1 1 14 2 13 1 1 1 1 1 3 1
2        17 0 0 1  1 10 0 2 0 6  6 1  1 2 4 2 3 1 3 2
3        18 1 0 0  1 11 0 2 0 0  1 1  5 0 7 0 6 1 6 5

I'm looking for your code and I'll write a little bit later. I do not know how to express my immense gratitude for your help!!! — StackQuestions, Oct 30 '19 at 10:30
If I break free this afternoon I'll put the easier solution... This one got complex for no reason — Carl Boneri, Oct 30 '19 at 10:50
1) I tested the code on big file of 24 mb and it took more than 10 minutes of work. I'm affraid this version is not faster than initial code. 2) One remark about result table. I need that colomn "attrs" has attribute value (like 020, 035, 245, etc) and not the attribute name "tag" or "code". Like in my example. In tag "subfield" only one attribute so I think it is not important to keep its name. As for later work, I intend to cast this table to have "attrs" like row names and "variable" as column names. But it is not actual task for the moment. The main thing - convert it to simple table. — StackQuestions, Oct 30 '19 at 11:11
if the attrs col has the value, then what actually goes in the variable col? — Carl Boneri, Oct 30 '19 at 11:14
Col "attrs" has value of attribute "tag" like 020, 035, 037, etc. from . Col "variable" has value of attribute "code" like "a", "z", "c", etc. from . — StackQuestions, Oct 30 '19 at 11:21
oh okay. so `attrs` is basically `@tag` and `variable` is basically `@code`? Why not just name them that? — Carl Boneri, Oct 30 '19 at 11:22
You are absolutely rigth. I used parts from another code and didn't make necessary changes. It is my mistake. — StackQuestions, Oct 30 '19 at 11:34
thank you very much for your help. Your code gave me some ideas how to partially solve the problem. I took time but finally I parsed it :) — StackQuestions, Oct 31 '19 at 15:58
You should add your working code to your original question to help future readers — Carl Boneri, Oct 31 '19 at 16:21
It is really messy and I don't think it could help somebody else. If I find better solution I'll post here. — StackQuestions, Oct 31 '19 at 19:31
you never know, whatever solution you found might guide somebody in the right direction. — Carl Boneri, Nov 01 '19 at 03:30
I could send my code to you but I can't see how write you. There is no any form of private letters or chats in the system... — StackQuestions, Nov 03 '19 at 18:47

Parsing xml data with R. The code is very slow. How to make it faster?

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