D3.js Simple Transistions

d3transistions1.js

function redraw() {
    chart.selectAll("rect")
      .data(data)
     .transition()
       .duration(1000)
       .attr("y", function(d) { return h - y(d) - .5; })
       .attr("height", function(d) { return y(d); } );  
}

d3transistions2.js

// replace an element in the data array with a new value
data[2] = 49;
redraw();