title: move 4 columns to one column, sort only index, not value
body: <p>I have OHLC dataseries, and I'd like to move to 'one' column series to sorting OHLC also.</p>
  <p>Datas:</p>
  <pre><code>                 Time      Open      High       Low     Close    Volume
  0 2022-04-30 13:05:00  38580.46  38610.44  38580.46  38610.44  33.14334
  1 2022-04-30 13:06:00  38610.43  38610.44  38600.00  38600.00  10.64336
  2 2022-04-30 13:07:00  38600.00  38604.17  38600.00  38604.16  11.41531
  3 2022-04-30 13:08:00  38604.16  38607.97  38604.16  38604.16   9.25056
  4 2022-04-30 13:09:00  38604.16  38606.81  38604.16  38606.80   6.83944
  5 2022-04-30 13:10:00  38606.81  38606.81  38602.00  38602.00   8.55118
  6 2022-04-30 13:11:00  38602.01  38602.01  38602.00  38602.01   6.45035
  7 2022-04-30 13:12:00  38602.01  38602.01  38600.28  38600.28   5.33661
  8 2022-04-30 13:13:00  38600.28  38606.80  38600.28  38606.80  11.11430
  9 2022-04-30 13:14:00  38606.80  38606.80  38600.56  38600.57   9.40830
  </code></pre>
  <p>I did it with for loop, but I think this very slow on big data.</p>
  <pre><code>df1 = pd.DataFrame(ohlcv, columns = ['Time', 'Open', 'High', 'Low', 'Close', 'Volume'])
  df_tick=pd.DataFrame(columns=['Time', 'Price', 'Volume'])
  
  for i in range(0,len(df1)):
      df_tick = pd.concat([df_tick, pd.DataFrame.from_records([{'Time': df1['Time'][i],'Price': df1['Open'][i]}])],ignore_index=True)
      df_tick = pd.concat([df_tick, pd.DataFrame.from_records([{'Time': df1['Time'][i],'Price': df1['High'][i]}])],ignore_index=True)
      df_tick = pd.concat([df_tick, pd.DataFrame.from_records([{'Time': df1['Time'][i],'Price': df1['Low'][i]}])],ignore_index=True)
      df_tick = pd.concat([df_tick, pd.DataFrame.from_records([{'Time': df1['Time'][i],'Price': df1['Close'][i]}])], ignore_index=True)
  </code></pre>
  <p>The destination data looks like this:</p>
  <pre><code>                   Time     Price Volume
  0   2022-04-30 13:05:00  38580.46    NaN
  1   2022-04-30 13:05:00  38610.44    NaN
  2   2022-04-30 13:05:00  38580.46    NaN
  3   2022-04-30 13:05:00  38610.44    NaN
  4   2022-04-30 13:06:00  38610.43    NaN
  5   2022-04-30 13:06:00  38610.44    NaN
  6   2022-04-30 13:06:00   38600.0    NaN
  7   2022-04-30 13:06:00   38600.0    NaN
  8   2022-04-30 13:07:00   38600.0    NaN
  9   2022-04-30 13:07:00  38604.17    NaN
  10  2022-04-30 13:07:00   38600.0    NaN
  11  2022-04-30 13:07:00  38604.16    NaN
  12  2022-04-30 13:08:00  38604.16    NaN
  13  2022-04-30 13:08:00  38607.97    NaN
  14  2022-04-30 13:08:00  38604.16    NaN
  15  2022-04-30 13:08:00  38604.16    NaN
  16  2022-04-30 13:09:00  38604.16    NaN
  17  2022-04-30 13:09:00  38606.81    NaN
  18  2022-04-30 13:09:00  38604.16    NaN
  </code></pre>
  <p>I tried with simple concat, but sorting with index, soring values also.</p>
  <pre><code>df_tick=pd.concat([df1['Open'], df1['High'],df1['Low'],df1['Close']], axis=0)
  df_tick=df_tick.sort_index()
  </code></pre>
  <p>How to sorting only index in the order of entry?</p>