title: Search values across all columns in R data frame
body: <p>Here's a sample data frame. </p>
  
  <pre><code>df = data.frame(company = c('a', 'b', 'c', 'd'),
                   bond = c(0.2, 1, 0.3, 0),
                   equity = c(0.7, 0, 0.5, 1),
                   cash = c(0.1, 0, 0.2, 0))
  df
  
    company bond equity cash
  1       a  0.2    0.7  0.1
  2       b  1.0    0.0  0.0
  3       c  0.3    0.5  0.2
  4       d  0.0    1.0  0.0
  </code></pre>
  
  <p>I need to find companies which have 1.0 in any columns. 
  The expected result should be <strong>b and d</strong>.</p>
  
  <p>Please provide a solution that works for >20 columns. 
  Solutions like <code>df %&gt;% filter(bond == 1)</code> only works for searching a particular column.</p>
  
  <p><code>dplyr</code> or <code>data.table</code> solutions are acceptable.</p>
  
  <p>Thanks.</p>