title: create a dataframe from 3 other dataframes in python
body: <p>I am trying to create a new df which summarises my key information, by taking that information from 3 (say) other dataframes.</p>
  
  <pre><code>dfdate = {'x1': [2, 4, 7, 5, 6],
       'x2': [2, 2, 2, 6, 7],
       'y1': [3, 1, 4, 5, 9]}
  dfdate = pd.DataFrame(df, index=range(0:4))
  
  dfqty = {'x1': [1, 2, 6, 6, 8],
       'x2': [3, 1, 1, 7, 5],
       'y1': [2, 4, 3, 2, 8]}
  dfqty = pd.DataFrame(df2, range(0:4))
  
  dfprices = {'x1': [0, 2, 2, 4, 4],
       'x2': [2, 0, 0, 3, 4],
       'y1': [1, 3, 2, 1, 3]}
  dfprices = pd.DataFrame(df3, range(0:4))
  </code></pre>
  
  <p>Let us say the above 3 dataframes are my data. Say, some dates, qty, and prices of goods. My new df is to be constructed from the above data:</p>
  
  <pre><code>rng = len(dfprices.columns)*len(dfprices.index) # This is the len of new df
  dfnew = pd.DataFrame(np.nan,index=range(0,rng),columns=['Letter', 'Number', 'date', 'qty', 'price])
  </code></pre>
  
  <p>Now, this is where I struggle to piece my stuff together. I am trying to take all the data in dfdate and put it into a column in the new df. same with dfqty and dfprice. (so 3x5 matricies essentially goto a 1x15 vector and are placed into the new df).</p>
  
  <p>As well as that, I need a couple of columns in dfnew as identifiers, from the names of the columns of the old df.</p>
  
  <p>Ive tried for loops but to no avail, and don't know how to convert a df to series. But my desired output is:</p>
  
  <pre><code>dfnew:
     'Lettercol','Numbercol', 'date', 'qty', 'price'
  0     X            1         2       1      0
  1     X            1         4       2      2
  2     X            1         7       6      2
  3     X            1         5       6      4
  4     X            1         6       8      4      
  5     X            2         2       3      2      
  6     X            2         2       1      0                   
  7     X            2         2       1      0                 
  8     X            2         6       7      3          
  9     X            2         7       5      4           
  10    Y            1         3       2      1                  
  11    Y            1         1       4      3           
  12    Y            1         4       3      2           
  13    Y            1         5       2      1          
  14    Y            1         9       8      3         
  </code></pre>
  
  <p>where the numbers 0-14 are the index.
  letter = letter from col header in DFs
  number = number from col header in DFs
  next 3 columns are data from the orig df's</p>
  
  <p>(don't ask why the original data is in that funny format :)</p>
  
  <p>thanks so much. my last Q wasn't well received so have tried to make this one better, thanks </p>