Question

我正在使用php＆amp; Charts.js根据html <select>生成数据图表我的问题是，即使从html <select>中没有选择任何内容，页面底部也会显示空白图表而不是显示echo块中的else {}语句。

如果从html <select>

中进行选择，我应该如何重写此语法，以便创建仅图表

<body>
    <form method="POST">
    <p>Select Sales Name:
            <select name="Name">
                <option value="">Select A Name...</option>
                <option value="Joe">Joe</option>
                <option value="Jack">Jack</option>
                <option value="Jerry">Jerry</option>
                <option value="Jimmy">Jimmy</option></select></p>
        <input type="submit" name="submit" value="Show Me">
    </form>
</body>
<?php
if (isset($_POST['submit'])) {
    $whatsalesprsn = $_POST['Name'];
    if ($whatsalesprsn == "Joe") { $region = "East"; }
    if ($whatsalesprsn == "Jack") { $region = "West"; }
    if ($whatsalesprsn == "Jerry") { $region = "North"; }
    if ($whatsalesprsn == "Jimmy") { $region = "South"; }
    if (isset($region)) {
        $query = "Select * from salesdata where salesregion = '$region'";
        $db->setQuery($query);
        $rows = $db->loadColumn();
        $output = array();
        for ($i = 0; $i <= 3; $i++) {
        $column = $db->loadColumn($i);
        array_push($output, $column);
    }
    $data = json_encode($output[0]);
    } else { echo "PLease select a sales person to display data for."; }
}
?>

<html>
    <head>
        <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.6.0/Chart.min.js"></script>
    </head>
    <body>
        <div id="container" style="width: 75%;">
            <canvas id="canvas"></canvas>
        </div><script>
            //JavaScript to generate chart
        </script>
    </body>
</html>

Answer 1

某处你必须致电new Chart(...)。如果你这样做而没有传递有效数据，那么Chart.js将创建一个空图表（因为这就是你告诉它要做的）。

如果您没有有效数据（即在<select>元素中没有选择任何内容），请不要实例化Chart.js。类似的东西：

if (data.length) {
    new Chart(...);
}

Answer 2

您需要使用empty()功能添加std::vector<float> test_features = {0.377745556,0.009904444,0.063231111,0.009904444,0.003734444,0.002914444,0.008633333,0.000471111,0.009642222,0.05406,0.050163333,7e-05,0.006528889,0.000314444,0.00649,0.043956667,0.016816667,0.001644444,0.016906667,0.00204,0.027342222,0.13864}; int n_features = test_features.size(); x= tf::Tensor(tf::DT_FLOAT, tf::TensorShape({1,n_features})); auto x_mapped = x.tensor<float, 2>(); for (int i = 0; i< n_features; i++) { x_mapped(0, i) = test_features[i]; }。如果if statement使用empty()函数

检查if statement变量是否为空，请{

$whatsalesprsn

如果PHP变量具有值，则仅生成图表

2 个答案: