title: Getting the first value from spark.sql.Row
body: <p>I have  the following json format :</p>
  
  <pre><code>{"Request": {"TrancheList": {"Tranche": [{"TrancheId": "500192163","OwnedAmt": "26500000",    "Curr": "USD" }, {  "TrancheId": "500213369", "OwnedAmt": "41000000","Curr": "USD"}]},"FxRatesList": {"FxRatesContract": [{"Currency": "CHF","FxRate": "0.97919983706115"},{"Currency": "AUD", "FxRate": "1.2966804979253"},{ "Currency": "USD","FxRate": "1"},{"Currency": "SEK","FxRate": "8.1561012531034"},{"Currency": "NOK", "FxRate": "8.2454981641398"},{"Currency": "JPY","FxRate": "111.79999785344"},{"Currency": "HKD","FxRate": "7.7568025218916"},{"Currency": "GBP","FxRate": "0.69425159677867"}, {"Currency": "EUR","FxRate": "0.88991723769689"},{"Currency": "DKK", "FxRate": "6.629598372301"}]},"isExcludeDeals": "true","baseCurrency": "USD"}}
  </code></pre>
  
  <p>The json is read from hdfs :</p>
  
  <pre><code>val hdfsRequest = spark.read.json("hdfs://localhost/user/request.json")
  val baseCurrency = hdfsRequest.select("Request.baseCurrency").map(_.getString(0)).collect.headOption
  var fxRates = hdfsRequest.select("Request.FxRatesList.FxRatesContract")
  val fxRatesDF = fxRates.select(explode(fxRates("FxRatesContract"))).toDF("FxRatesContract").select("FxRatesContract.Currency", "FxRatesContract.FxRate").filter($"Currency"===baseCurrency.get)
  fxRatesDF.show()
  </code></pre>
  
  <p>The output that I am getting for fxRatesDF is :</p>
  
  <pre><code>fxRatesDF: org.apache.spark.sql.Dataset[org.apache.spark.sql.Row] = [Currency: string, FxRate: string]
  +--------+------+
  |Currency|FxRate|
  +--------+------+
  |     USD|     1|
  </code></pre>
  
  <p>How can I grab the value of first row of Fxrate column?</p>