引用 PHP 数组的未定义索引错误

Question

我在尝试迭代一些数据时遇到错误，我无法弄清楚我做错了什么。这是我从 API 请求返回的数据格式：

Array
(
    [search-results] => Array
        (
            [entry] => Array
                (
                    [0] => Array
                        (
                            [author] => Array
                                (
                                    [0] => Array
                                        (
                                            [authname] => Griffin J.
                                            [surname] => Griffin
                                            [initials] => J.M.
                                        )
                                    [1] => Array
                                        (
                                            [authname] => Williams D.
                                            [surname] => Williams
                                            [initials] => D.H.
                                        )
                                )
                        )
                    [1] => Array
                        ( ...etc...
                        )
                )
        )
)

以上数据打印输出来自下面代码中的$eachJson作为参考。

我一次只能执行一个 API 请求来获取 100 个结果，因此我设置了一个 for 循环来执行搜索 100 次，然后执行下一个 100 次等。由于每条记录有多个 authors，我设置了一个foreach 循环来迭代作者，这就是我收到错误消息的地方：

Notice: Undefined index: author in C:\xampp\htdocs\academic_intelligence\public\ScopusTest.php on line 42

Warning: Invalid argument supplied for foreach() in C:\xampp\htdocs\academic_intelligence\public\ScopusTest.php on line 42

代码如下：

$apiKey = "&apiKey=c2cb86c3a511ed34dd6f03f481c637c1";
$search1 = urlencode("badgers");
$search2 = urlencode(" OR weasels");
$start = 0;
$scopusData = [];
// create an array to represent citation values to ignore, i.e. not interested
// in any publications with less than 4 citations
$ignore = array(0, 1, 2, 3);

// set processing time for browser before timeout
ini_set('max_execution_time', 3600);
// override default PHP memory limit
ini_set('memory_limit', '-1');

// REST HTTP GET Request searching for people associated with keywords (term)
$searchLink = "http://api.elsevier.com/content/search/scopus?query=KEY(" . $search1 . $search2 . ")" . $apiKey . "&sort=citedby-count&count=100&start=" . $start . "&view=complete";

// save results to a variable
$searchResponse = file_get_contents($searchLink);

// convert JSON to PHP variable
$searchJson = json_decode($searchResponse, true);

// get total number of results for query to know when to stop iterating data
$total = $searchJson['search-results']['opensearch:totalResults'];

// iterate data loading next 200 results (max) each time and adding new results to array
for ($i = $start; $i <= $total; $i+=100) {
    // REST HTTP GET Request searching for people associated with keywords (term)
    $eachLink = "http://api.elsevier.com/content/search/scopus?query=KEY(" . $search1 . $search2 . ")" . $apiKey . "&sort=citedby-count&count=100&start=" . $i . "&view=complete";

    // save results to a variable
    $eachResponse = file_get_contents($eachLink);

    $eachJson = json_decode($eachResponse, true);

    foreach ($eachJson['search-results']['entry'] as $record) {
        // array to store authors
        $authors = [];
        foreach ($record['author'] as $thisAuthor) { // **LINE 42**
            // push initials and surname to array
            array_push($authors, ($thisAuthor['initials'] . $thisAuthor['surname']));
        };
        // scopus ID
        $scopusID = $record['dc:identifier'];
        // paper title
        $title = $record['dc:title'];
        // date
        $date = substr($record['prism:coverDate'], 0, 4);
        // citations, if less than 4 then break out of iteration
        if (!in_array(($cites = $record['citedby-count']), $ignore)) {
            $cites = $record['citedby-count'];
        } else {
            break 2;
        }

        $thisData = [
                        "authors" => $authors,
                        "ID"      => $scopusID,
                        "title"   => $title,
                        "date"    => $date,
                        "cites"   => $cites
        ];

        array_push($scopusData, $thisData);
    }
};

// need to replace single quotes to avoid char escape
for ($i = 0; $i < count($scopusData); $i++) {
    foreach ($scopusData[$i]['authors'] as &$edit) {
        $edit = str_replace("'", "", $edit);
    };
    $scopusData[$i]['title'] = str_replace("'", "", $scopusData[$i]['title']);
};

我已突出显示导致错误的第 42 行。这一定很简单，但这是漫长的一天，我无法弄清楚问题所在！最后我仍然得到正确的数据，最终数组 scopusData 包括从错误的 foreach 循环中获取的所有作者，所以我收到错误似乎很奇怪。

Answer 1

您确定每条记录都包含作者元素吗？

也许你应该在 foreach() 循环之前添加一个 ifset($record['author'])。

^{（根据 OP 的要求重新发表评论作为答案）}