title: Problems with making my dataframe in 'wide' structure while trying using spread() function in R
body: <p>I'm trying to use <code>spread()</code> function to make my data.frame wide, but i have some errors that i don't even understand...</p>
  
  <p>some part of my dataframe is looks like this:</p>
  
  <pre><code>&gt; df
      NO2 Month
  1    23    01
  2    27    01
  3    16    01
  4    13    01
  5    26    01
  6    23    01
  7    51    01
  8    46    01
  9    21    01
  10   18    01
  11   13    01
  12   22    01
  13   47    01
  14   60    01
  15   49    01
  16   76    01
  17   38    01
  18   24    01
  19   15    01
  20   20    01
  21   33    01
  22   17    01
  23   19    01
  24   20    01
  25   25    01
  26   46    01
  27   53    01
  28   41    01
  29   54    01
  30   28    01
  31   28    01
  32   51    02
  33   61    02
  34   56    02
  35   57    02
  36   30    02
  37   12    02
  38   27    02
  39   13    02
  40   35    02
  41   40    02
  42   40    02
  43   47    02
  44   72    02
  45   55    02
  46   30    02
  47   10    02
  48   29    02
  49   50    02
  50   39    02
  51   61    02
  52   56    02
  53   44    02
  54   46    02
  55   35    02
  56   34    02
  57   41    02
  58   39    02
  59   39    02
  60   27    03
  61   48    03
  62   36    03
  63   40    03
  64   41    03
  65   45    03
  66   46    03
  67   43    03
  68   55    03 (...)
  </code></pre>
  
  <p>so simply i have values for each day in year and i want to spread them and use boxplot() for each month, to make it more clearly to read, but since i cant event spread it i cant show it in right way</p>
  
  <p>I'm trying the spread and also reshape but have some errors:</p>
  
  <pre><code>df=data.frame(data)
  df$Month=as.numeric(format(data$date,format="%m"))
  df=df%&gt;%select(c("NO2","Month"))
  
  df=reshape(df,idvar=c("NO2","Month"),direction="wide",timevar="Month")
  warnings() ## here i have first errors (will show them in below)
  
  df=spread(df,Month,NO2)  ## have problems here also
  
  df=spread(df,df$Month,df$NO2)  ## and here also
  </code></pre>
  
  <p>First error i have with <code>reshape()</code> function is for each "Month" i've got something like this</p>
  
  <pre><code>1: In reshapeWide(data, idvar = idvar, timevar = timevar,  ... :
    multiple rows match for Month=1: first taken
  </code></pre>
  
  <p>for second error i have something like this</p>
  
  <pre><code>Error in eval_tidy(enquo(var), var_env) : object 'Month' not found
  </code></pre>
  
  <p>and for third try i have this</p>
  
  <pre><code>Error: "var" must evaluate to a single number or a column name, not NULL
  </code></pre>
  
  <p>Can someone help me? I don't rlly get it, i've made spreads and this is my first touch with this problem..</p>