title: How can I make a list object to dataframe in long format with tidyverse in R
body: <pre><code>dd &lt;- list(c("2020-1-2","SDF","fff,33"),
             c("2020-1-3","KKK","ffd,23","fffdf,23","ssfds,43"))
  dd
  # [[1]]
  # [1] "2020-1-2" "SDF"      "fff,33"  
  
  # [[2]]
  # [1] "2020-1-3" "KKK"      "ffd,23"   "fffdf,23" "ssfds,43"
  
  ddtarget &lt;- data.frame(date= c("2020-1-2","2020-1-3","2020-1-3","2020-1-3"),
                         category = c("SDF","KKK","KKK","KKK"),
                         element = c("fff,33","ffd,23","fffdf,23","ssfds,43"))
  ddtarget
  #       date category  element
  # 1 2020-1-2      SDF   fff,33
  # 2 2020-1-3      KKK   ffd,23
  # 3 2020-1-3      KKK fffdf,23
  # 4 2020-1-3      KKK ssfds,43
  </code></pre>
  
  <p>I want to transform dd to ddtarget with tidyverse such as map() or similar functions, but I can not make it by myself. Can anyone help me? </p>