title: How can i match values inside the same dataframe?
body: <p>My dataframe looks like the following:</p>
  <pre><code>  destination origen iso3_exp Importer    flow      iso3_imp    gdp_o      gdp_d      distw  año
  1    ABW    AUT       40      533    188.782      ABW 240457629696 1320670336  8632.9708 1995
  2    AUT    ABW       58      533    912.362      ABW 289122615296 1320670336  7843.2555 1995
  3    CHL    ARG       76      533   4535.649      ABW 768951320576 1320670336  4431.5712 1995
  4    ARG    CHL      156      533    496.458      ABW 728007573504 1320670336 14590.9239 1995
  5    AUT    BEL      170      533 116442.845      ABW  92507275264 1320670336   929.5887 1995
  </code></pre>
  <p>I need to create a variable called totalflow that is the sum the variable &quot;flow&quot; between the rows that matches Origen-Destination, for example: the row 3 has Destination to CHL and Origen from ARG, and the row 4 has the destination to ARG and origen from CHL i need tu sum the flow of that row (3) with the flow of the row 4 and do the same to all the other rows.</p>
  <pre><code>  destination origen iso3_exp Importer    flow      iso3_imp    gdp_o      gdp_d  distw  año   totalflow
  1    ABW    AUT       40      533      188.782      ABW 240457629696 1320670336  8632.9708 1995  1100
  2    AUT    ABW       58      533      912.362      ABW 289122615296 1320670336  7843.2555 1995  1100
  3    CHL    ARG       76      533     4535.649      ABW 768951320576 1320670336  4431.5712 1995  5031
  4    ARG    CHL      156      533      496.458      ABW 728007573504 1320670336 14590.9239 1995  5031
  5    AUT    BEL      170      533   116442.845      ABW  92507275264 1320670336   929.5887 1995 116442
  </code></pre>
  <p>Thanks beforehand.</p>