我在数据框（要素类型）中有一列我要使用POSIXlt转换为strptime()。我正在做的是：
file[, 2] <- strptime(file[, 2], format="%H:%M:%S")
列中的值示例为：17:24:00 17:25:00 17:26:00
但是，该函数返回全0。格式指定不正确吗？任何帮助将不胜感激。
这是dput(head(file[,2]))的输出：
structure(1045:1050, .Label = c("00:00:00", "00:01:00", "00:02:00",
"00:03:00", "00:04:00", "00:05:00", "00:06:00", "00:07:00", "00:08:00",
"00:09:00", "00:10:00", "00:11:00", "00:12:00", "00:13:00", "00:14:00",
"00:15:00", "00:16:00", "00:17:00", "00:18:00", "00:19:00", "00:20:00",
"00:21:00", "00:22:00", "00:23:00", "00:24:00", "00:25:00", "00:26:00",
"00:27:00", "00:28:00", "00:29:00", "00:30:00", "00:31:00", "00:32:00",
"00:33:00", "00:34:00", "00:35:00", "00:36:00", "00:37:00", "00:38:00",
"00:39:00", "00:40:00", "00:41:00", "00:42:00", "00:43:00", "00:44:00",
"00:45:00", "00:46:00", "00:47:00", "00:48:00", "00:49:00", "00:50:00",
"00:51:00", "00:52:00", "00:53:00", "00:54:00", "00:55:00", "00:56:00",
"00:57:00", "00:58:00", "00:59:00", "01:00:00", "01:01:00", "01:02:00",
"01:03:00", "01:04:00", "01:05:00", "01:06:00", "01:07:00", "01:08:00",
"01:09:00", "01:10:00", "01:11:00", "01:12:00", "01:13:00", "01:14:00",
"01:15:00", "01:16:00", "01:17:00", "01:18:00", "01:19:00", "01:20:00",
"01:21:00", "01:22:00", "01:23:00", "01:24:00", "01:25:00", "01:26:00",
"01:27:00", "01:28:00", "01:29:00", "01:30:00", "01:31:00", "01:32:00",
"01:33:00", "01:34:00", "01:35:00", "01:36:00", "01:37:00", "01:38:00",
"01:39:00", "01:40:00", "01:41:00", "01:42:00", "01:43:00", "01:44:00",
"01:45:00", "01:46:00", "01:47:00", "01:48:00", "01:49:00", "01:50:00",
"01:51:00", "01:52:00", "01:53:00", "01:54:00", "01:55:00", "01:56:00",
"01:57:00", "01:58:00", "01:59:00", "02:00:00", "02:01:00", "02:02:00",
"02:03:00", "02:04:00", "02:05:00", "02:06:00", "02:07:00", "02:08:00",
"02:09:00", "02:10:00", "02:11:00", "02:12:00", "02:13:00", "02:14:00",
"02:15:00", "02:16:00", "02:17:00", "02:18:00", "02:19:00", "02:20:00",
"02:21:00", "02:22:00", "02:23:00", "02:24:00", "02:25:00", "02:26:00",
"02:27:00", "02:28:00", "02:29:00", "02:30:00", "02:31:00", "02:32:00",
"02:33:00", "02:34:00", "02:35:00", "02:36:00", "02:37:00", "02:38:00",
"02:39:00", "02:40:00", "02:41:00", "02:42:00", "02:43:00", "02:44:00",
"02:45:00", "02:46:00", "02:47:00", "02:48:00", "02:49:00", "02:50:00",
"02:51:00", "02:52:00", "02:53:00", "02:54:00", "02:55:00", "02:56:00",
"02:57:00", "02:58:00", "02:59:00", "03:00:00", "03:01:00", "03:02:00",
"03:03:00", "03:04:00", "03:05:00", "03:06:00", "03:07:00", "03:08:00",
"03:09:00", "03:10:00", "03:11:00", "03:12:00", "03:13:00", "03:14:00",
"03:15:00", "03:16:00", "03:17:00", "03:18:00", "03:19:00", "03:20:00",
"03:21:00", "03:22:00", "03:23:00", "03:24:00", "03:25:00", "03:26:00",
"03:27:00", "03:28:00", "03:29:00", "03:30:00", "03:31:00", "03:32:00",
"03:33:00", "03:34:00", "03:35:00", "03:36:00", "03:37:00", "03:38:00",
"03:39:00", "03:40:00", "03:41:00", "03:42:00", "03:43:00", "03:44:00",
"03:45:00", "03:46:00", "03:47:00", "03:48:00", "03:49:00", "03:50:00",
"03:51:00", "03:52:00", "03:53:00", "03:54:00", "03:55:00", "03:56:00",
"03:57:00", "03:58:00", "03:59:00", "04:00:00", "04:01:00", "04:02:00",
"04:03:00", "04:04:00", "04:05:00", "04:06:00", "04:07:00", "04:08:00",
"04:09:00", "04:10:00", "04:11:00", "04:12:00", "04:13:00", "04:14:00",
"04:15:00", "04:16:00", "04:17:00", "04:18:00", "04:19:00", "04:20:00",
"04:21:00", "04:22:00", "04:23:00", "04:24:00", "04:25:00", "04:26:00",
"04:27:00", "04:28:00", "04:29:00", "04:30:00", "04:31:00", "04:32:00",
"04:33:00", "04:34:00", "04:35:00", "04:36:00", "04:37:00", "04:38:00",
"04:39:00", "04:40:00", "04:41:00", "04:42:00", "04:43:00", "04:44:00",
"04:45:00", "04:46:00", "04:47:00", "04:48:00", "04:49:00", "04:50:00",
"04:51:00", "04:52:00", "04:53:00", "04:54:00", "04:55:00", "04:56:00",
"04:57:00", "04:58:00", "04:59:00", "05:00:00", "05:01:00", "05:02:00",
"05:03:00", "05:04:00", "05:05:00", "05:06:00", "05:07:00", "05:08:00",
"05:09:00", "05:10:00", "05:11:00", "05:12:00", "05:13:00", "05:14:00",
"05:15:00", "05:16:00", "05:17:00", "05:18:00", "05:19:00", "05:20:00",
"05:21:00", "05:22:00", "05:23:00", "05:24:00", "05:25:00", "05:26:00",
"05:27:00", "05:28:00", "05:29:00", "05:30:00", "05:31:00", "05:32:00",
"05:33:00", "05:34:00", "05:35:00", "05:36:00", "05:37:00", "05:38:00",
"05:39:00", "05:40:00", "05:41:00", "05:42:00", "05:43:00", "05:44:00",
"05:45:00", "05:46:00", "05:47:00", "05:48:00", "05:49:00", "05:50:00",
"05:51:00", "05:52:00", "05:53:00", "05:54:00", "05:55:00", "05:56:00",
"05:57:00", "05:58:00", "05:59:00", "06:00:00", "06:01:00", "06:02:00",
"06:03:00", "06:04:00", "06:05:00", "06:06:00", "06:07:00", "06:08:00",
"06:09:00", "06:10:00", "06:11:00", "06:12:00", "06:13:00", "06:14:00",
"06:15:00", "06:16:00", "06:17:00", "06:18:00", "06:19:00", "06:20:00",
"06:21:00", "06:22:00", "06:23:00", "06:24:00", "06:25:00", "06:26:00",
"06:27:00", "06:28:00", "06:29:00", "06:30:00", "06:31:00", "06:32:00",
"06:33:00", "06:34:00", "06:35:00", "06:36:00", "06:37:00", "06:38:00",
"06:39:00", "06:40:00", "06:41:00", "06:42:00", "06:43:00", "06:44:00",
"06:45:00", "06:46:00", "06:47:00", "06:48:00", "06:49:00", "06:50:00",
"06:51:00", "06:52:00", "06:53:00", "06:54:00", "06:55:00", "06:56:00",
"06:57:00", "06:58:00", "06:59:00", "07:00:00", "07:01:00", "07:02:00",
"07:03:00", "07:04:00", "07:05:00", "07:06:00", "07:07:00", "07:08:00",
"07:09:00", "07:10:00", "07:11:00", "07:12:00", "07:13:00", "07:14:00",
"07:15:00", "07:16:00", "07:17:00", "07:18:00", "07:19:00", "07:20:00",
"07:21:00", "07:22:00", "07:23:00", "07:24:00", "07:25:00", "07:26:00",
"07:27:00", "07:28:00", "07:29:00", "07:30:00", "07:31:00", "07:32:00",
"07:33:00", "07:34:00", "07:35:00", "07:36:00", "07:37:00", "07:38:00",
"07:39:00", "07:40:00", "07:41:00", "07:42:00", "07:43:00", "07:44:00",
"07:45:00", "07:46:00", "07:47:00", "07:48:00", "07:49:00", "07:50:00",
"07:51:00", "07:52:00", "07:53:00", "07:54:00", "07:55:00", "07:56:00",
"07:57:00", "07:58:00", "07:59:00", "08:00:00", "08:01:00", "08:02:00",
"08:03:00", "08:04:00", "08:05:00", "08:06:00", "08:07:00", "08:08:00",
"08:09:00", "08:10:00", "08:11:00", "08:12:00", "08:13:00", "08:14:00",
"08:15:00", "08:16:00", "08:17:00", "08:18:00", "08:19:00", "08:20:00",
"08:21:00", "08:22:00", "08:23:00", "08:24:00", "08:25:00", "08:26:00",
"08:27:00", "08:28:00", "08:29:00", "08:30:00", "08:31:00", "08:32:00",
"08:33:00", "08:34:00", "08:35:00", "08:36:00", "08:37:00", "08:38:00",
"08:39:00", "08:40:00", "08:41:00", "08:42:00", "08:43:00", "08:44:00",
"08:45:00", "08:46:00", "08:47:00", "08:48:00", "08:49:00", "08:50:00",
"08:51:00", "08:52:00", "08:53:00", "08:54:00", "08:55:00", "08:56:00",
"08:57:00", "08:58:00", "08:59:00", "09:00:00", "09:01:00", "09:02:00",
"09:03:00", "09:04:00", "09:05:00", "09:06:00", "09:07:00", "09:08:00",
"09:09:00", "09:10:00", "09:11:00", "09:12:00", "09:13:00", "09:14:00",
"09:15:00", "09:16:00", "09:17:00", "09:18:00", "09:19:00", "09:20:00",
"09:21:00", "09:22:00", "09:23:00", "09:24:00", "09:25:00", "09:26:00",
"09:27:00", "09:28:00", "09:29:00", "09:30:00", "09:31:00", "09:32:00",
"09:33:00", "09:34:00", "09:35:00", "09:36:00", "09:37:00", "09:38:00",
"09:39:00", "09:40:00", "09:41:00", "09:42:00", "09:43:00", "09:44:00",
"09:45:00", "09:46:00", "09:47:00", "09:48:00", "09:49:00", "09:50:00",
"09:51:00", "09:52:00", "09:53:00", "09:54:00", "09:55:00", "09:56:00",
"09:57:00", "09:58:00", "09:59:00", "10:00:00", "10:01:00", "10:02:00",
"10:03:00", "10:04:00", "10:05:00", "10:06:00", "10:07:00", "10:08:00",
"10:09:00", "10:10:00", "10:11:00", "10:12:00", "10:13:00", "10:14:00",
"10:15:00", "10:16:00", "10:17:00", "10:18:00", "10:19:00", "10:20:00",
"10:21:00", "10:22:00", "10:23:00", "10:24:00", "10:25:00", "10:26:00",
"10:27:00", "10:28:00", "10:29:00", "10:30:00", "10:31:00", "10:32:00",
"10:33:00", "10:34:00", "10:35:00", "10:36:00", "10:37:00", "10:38:00",
"10:39:00", "10:40:00", "10:41:00", "10:42:00", "10:43:00", "10:44:00",
"10:45:00", "10:46:00", "10:47:00", "10:48:00", "10:49:00", "10:50:00",
"10:51:00", "10:52:00", "10:53:00", "10:54:00", "10:55:00", "10:56:00",
"10:57:00", "10:58:00", "10:59:00", "11:00:00", "11:01:00", "11:02:00",
"11:03:00", "11:04:00", "11:05:00", "11:06:00", "11:07:00", "11:08:00",
"11:09:00", "11:10:00", "11:11:00", "11:12:00", "11:13:00", "11:14:00",
"11:15:00", "11:16:00", "11:17:00", "11:18:00", "11:19:00", "11:20:00",
"11:21:00", "11:22:00", "11:23:00", "11:24:00", "11:25:00", "11:26:00",
"11:27:00", "11:28:00", "11:29:00", "11:30:00", "11:31:00", "11:32:00",
"11:33:00", "11:34:00", "11:35:00", "11:36:00", "11:37:00", "11:38:00",
"11:39:00", "11:40:00", "11:41:00", "11:42:00", "11:43:00", "11:44:00",
"11:45:00", "11:46:00", "11:47:00", "11:48:00", "11:49:00", "11:50:00",
"11:51:00", "11:52:00", "11:53:00", "11:54:00", "11:55:00", "11:56:00",
"11:57:00", "11:58:00", "11:59:00", "12:00:00", "12:01:00", "12:02:00",
"12:03:00", "12:04:00", "12:05:00", "12:06:00", "12:07:00", "12:08:00",
"12:09:00", "12:10:00", "12:11:00", "12:12:00", "12:13:00", "12:14:00",
"12:15:00", "12:16:00", "12:17:00", "12:18:00", "12:19:00", "12:20:00",
"12:21:00", "12:22:00", "12:23:00", "12:24:00", "12:25:00", "12:26:00",
"12:27:00", "12:28:00", "12:29:00", "12:30:00", "12:31:00", "12:32:00",
"12:33:00", "12:34:00", "12:35:00", "12:36:00", "12:37:00", "12:38:00",
"12:39:00", "12:40:00", "12:41:00", "12:42:00", "12:43:00", "12:44:00",
"12:45:00", "12:46:00", "12:47:00", "12:48:00", "12:49:00", "12:50:00",
"12:51:00", "12:52:00", "12:53:00", "12:54:00", "12:55:00", "12:56:00",
"12:57:00", "12:58:00", "12:59:00", "13:00:00", "13:01:00", "13:02:00",
"13:03:00", "13:04:00", "13:05:00", "13:06:00", "13:07:00", "13:08:00",
"13:09:00", "13:10:00", "13:11:00", "13:12:00", "13:13:00", "13:14:00",
"13:15:00", "13:16:00", "13:17:00", "13:18:00", "13:19:00", "13:20:00",
"13:21:00", "13:22:00", "13:23:00", "13:24:00", "13:25:00", "13:26:00",
"13:27:00", "13:28:00", "13:29:00", "13:30:00", "13:31:00", "13:32:00",
"13:33:00", "13:34:00", "13:35:00", "13:36:00", "13:37:00", "13:38:00",
"13:39:00", "13:40:00", "13:41:00", "13:42:00", "13:43:00", "13:44:00",
"13:45:00", "13:46:00", "13:47:00", "13:48:00", "13:49:00", "13:50:00",
"13:51:00", "13:52:00", "13:53:00", "13:54:00", "13:55:00", "13:56:00",
"13:57:00", "13:58:00", "13:59:00", "14:00:00", "14:01:00", "14:02:00",
"14:03:00", "14:04:00", "14:05:00", "14:06:00", "14:07:00", "14:08:00",
"14:09:00", "14:10:00", "14:11:00", "14:12:00", "14:13:00", "14:14:00",
"14:15:00", "14:16:00", "14:17:00", "14:18:00", "14:19:00", "14:20:00",
"14:21:00", "14:22:00", "14:23:00", "14:24:00", "14:25:00", "14:26:00",
"14:27:00", "14:28:00", "14:29:00", "14:30:00", "14:31:00", "14:32:00",
"14:33:00", "14:34:00", "14:35:00", "14:36:00", "14:37:00", "14:38:00",
"14:39:00", "14:40:00", "14:41:00", "14:42:00", "14:43:00", "14:44:00",
"14:45:00", "14:46:00", "14:47:00", "14:48:00", "14:49:00", "14:50:00",
"14:51:00", "14:52:00", "14:53:00", "14:54:00", "14:55:00", "14:56:00",
"14:57:00", "14:58:00", "14:59:00", "15:00:00", "15:01:00", "15:02:00",
"15:03:00", "15:04:00", "15:05:00", "15:06:00", "15:07:00", "15:08:00",
"15:09:00", "15:10:00", "15:11:00", "15:12:00", "15:13:00", "15:14:00",
"15:15:00", "15:16:00", "15:17:00", "15:18:00", "15:19:00", "15:20:00",
"15:21:00", "15:22:00", "15:23:00", "15:24:00", "15:25:00", "15:26:00",
"15:27:00", "15:28:00", "15:29:00", "15:30:00", "15:31:00", "15:32:00",
"15:33:00", "15:34:00", "15:35:00", "15:36:00", "15:37:00", "15:38:00",
"15:39:00", "15:40:00", "15:41:00", "15:42:00", "15:43:00", "15:44:00",
"15:45:00", "15:46:00", "15:47:00", "15:48:00", "15:49:00", "15:50:00",
"15:51:00", "15:52:00", "15:53:00", "15:54:00", "15:55:00", "15:56:00",
"15:57:00", "15:58:00", "15:59:00", "16:00:00", "16:01:00", "16:02:00",
"16:03:00", "16:04:00", "16:05:00", "16:06:00", "16:07:00", "16:08:00",
"16:09:00", "16:10:00", "16:11:00", "16:12:00", "16:13:00", "16:14:00",
"16:15:00", "16:16:00", "16:17:00", "16:18:00", "16:19:00", "16:20:00",
"16:21:00", "16:22:00", "16:23:00", "16:24:00", "16:25:00", "16:26:00",
"16:27:00", "16:28:00", "16:29:00", "16:30:00", "16:31:00", "16:32:00",
"16:33:00", "16:34:00", "16:35:00", "16:36:00", "16:37:00", "16:38:00",
"16:39:00", "16:40:00", "16:41:00", "16:42:00", "16:43:00", "16:44:00",
"16:45:00", "16:46:00", "16:47:00", "16:48:00", "16:49:00", "16:50:00",
"16:51:00", "16:52:00", "16:53:00", "16:54:00", "16:55:00", "16:56:00",
"16:57:00", "16:58:00", "16:59:00", "17:00:00", "17:01:00", "17:02:00",
"17:03:00", "17:04:00", "17:05:00", "17:06:00", "17:07:00", "17:08:00",
"17:09:00", "17:10:00", "17:11:00", "17:12:00", "17:13:00", "17:14:00",
"17:15:00", "17:16:00", "17:17:00", "17:18:00", "17:19:00", "17:20:00",
"17:21:00", "17:22:00", "17:23:00", "17:24:00", "17:25:00", "17:26:00",
"17:27:00", "17:28:00", "17:29:00", "17:30:00", "17:31:00", "17:32:00",
"17:33:00", "17:34:00", "17:35:00", "17:36:00", "17:37:00", "17:38:00",
"17:39:00", "17:40:00", "17:41:00", "17:42:00", "17:43:00", "17:44:00",
"17:45:00", "17:46:00", "17:47:00", "17:48:00", "17:49:00", "17:50:00",
"17:51:00", "17:52:00", "17:53:00", "17:54:00", "17:55:00", "17:56:00",
"17:57:00", "17:58:00", "17:59:00", "18:00:00", "18:01:00", "18:02:00",
"18:03:00", "18:04:00", "18:05:00", "18:06:00", "18:07:00", "18:08:00",
"18:09:00", "18:10:00", "18:11:00", "18:12:00", "18:13:00", "18:14:00",
"18:15:00", "18:16:00", "18:17:00", "18:18:00", "18:19:00", "18:20:00",
"18:21:00", "18:22:00", "18:23:00", "18:24:00", "18:25:00", "18:26:00",
"18:27:00", "18:28:00", "18:29:00", "18:30:00", "18:31:00", "18:32:00",
"18:33:00", "18:34:00", "18:35:00", "18:36:00", "18:37:00", "18:38:00",
"18:39:00", "18:40:00", "18:41:00", "18:42:00", "18:43:00", "18:44:00",
"18:45:00", "18:46:00", "18:47:00", "18:48:00", "18:49:00", "18:50:00",
"18:51:00", "18:52:00", "18:53:00", "18:54:00", "18:55:00", "18:56:00",
"18:57:00", "18:58:00", "18:59:00", "19:00:00", "19:01:00", "19:02:00",
"19:03:00", "19:04:00", "19:05:00", "19:06:00", "19:07:00", "19:08:00",
"19:09:00", "19:10:00", "19:11:00", "19:12:00", "19:13:00", "19:14:00",
"19:15:00", "19:16:00", "19:17:00", "19:18:00", "19:19:00", "19:20:00",
"19:21:00", "19:22:00", "19:23:00", "19:24:00", "19:25:00", "19:26:00",
"19:27:00", "19:28:00", "19:29:00", "19:30:00", "19:31:00", "19:32:00",
"19:33:00", "19:34:00", "19:35:00", "19:36:00", "19:37:00", "19:38:00",
"19:39:00", "19:40:00", "19:41:00", "19:42:00", "19:43:00", "19:44:00",
"19:45:00", "19:46:00", "19:47:00", "19:48:00", "19:49:00", "19:50:00",
"19:51:00", "19:52:00", "19:53:00", "19:54:00", "19:55:00", "19:56:00",
"19:57:00", "19:58:00", "19:59:00", "20:00:00", "20:01:00", "20:02:00",
"20:03:00", "20:04:00", "20:05:00", "20:06:00", "20:07:00", "20:08:00",
"20:09:00", "20:10:00", "20:11:00", "20:12:00", "20:13:00", "20:14:00",
"20:15:00", "20:16:00", "20:17:00", "20:18:00", "20:19:00", "20:20:00",
"20:21:00", "20:22:00", "20:23:00", "20:24:00", "20:25:00", "20:26:00",
"20:27:00", "20:28:00", "20:29:00", "20:30:00", "20:31:00", "20:32:00",
"20:33:00", "20:34:00", "20:35:00", "20:36:00", "20:37:00", "20:38:00",
"20:39:00", "20:40:00", "20:41:00", "20:42:00", "20:43:00", "20:44:00",
"20:45:00", "20:46:00", "20:47:00", "20:48:00", "20:49:00", "20:50:00",
"20:51:00", "20:52:00", "20:53:00", "20:54:00", "20:55:00", "20:56:00",
"20:57:00", "20:58:00", "20:59:00", "21:00:00", "21:01:00", "21:02:00",
"21:03:00", "21:04:00", "21:05:00", "21:06:00", "21:07:00", "21:08:00",
"21:09:00", "21:10:00", "21:11:00", "21:12:00", "21:13:00", "21:14:00",
"21:15:00", "21:16:00", "21:17:00", "21:18:00", "21:19:00", "21:20:00",
"21:21:00", "21:22:00", "21:23:00", "21:24:00", "21:25:00", "21:26:00",
"21:27:00", "21:28:00", "21:29:00", "21:30:00", "21:31:00", "21:32:00",
"21:33:00", "21:34:00", "21:35:00", "21:36:00", "21:37:00", "21:38:00",
"21:39:00", "21:40:00", "21:41:00", "21:42:00", "21:43:00", "21:44:00",
"21:45:00", "21:46:00", "21:47:00", "21:48:00", "21:49:00", "21:50:00",
"21:51:00", "21:52:00", "21:53:00", "21:54:00", "21:55:00", "21:56:00",
"21:57:00", "21:58:00", "21:59:00", "22:00:00", "22:01:00", "22:02:00",
"22:03:00", "22:04:00", "22:05:00", "22:06:00", "22:07:00", "22:08:00",
"22:09:00", "22:10:00", "22:11:00", "22:12:00", "22:13:00", "22:14:00",
"22:15:00", "22:16:00", "22:17:00", "22:18:00", "22:19:00", "22:20:00",
"22:21:00", "22:22:00", "22:23:00", "22:24:00", "22:25:00", "22:26:00",
"22:27:00", "22:28:00", "22:29:00", "22:30:00", "22:31:00", "22:32:00",
"22:33:00", "22:34:00", "22:35:00", "22:36:00", "22:37:00", "22:38:00",
"22:39:00", "22:40:00", "22:41:00", "22:42:00", "22:43:00", "22:44:00",
"22:45:00", "22:46:00", "22:47:00", "22:48:00", "22:49:00", "22:50:00",
"22:51:00", "22:52:00", "22:53:00", "22:54:00", "22:55:00", "22:56:00",
"22:57:00", "22:58:00", "22:59:00", "23:00:00", "23:01:00", "23:02:00",
"23:03:00", "23:04:00", "23:05:00", "23:06:00", "23:07:00", "23:08:00",
"23:09:00", "23:10:00", "23:11:00", "23:12:00", "23:13:00", "23:14:00",
"23:15:00", "23:16:00", "23:17:00", "23:18:00", "23:19:00", "23:20:00",
"23:21:00", "23:22:00", "23:23:00", "23:24:00", "23:25:00", "23:26:00",
"23:27:00", "23:28:00", "23:29:00", "23:30:00", "23:31:00", "23:32:00",
"23:33:00", "23:34:00", "23:35:00", "23:36:00", "23:37:00", "23:38:00",
"23:39:00", "23:40:00", "23:41:00", "23:42:00", "23:43:00", "23:44:00",
"23:45:00", "23:46:00", "23:47:00", "23:48:00", "23:49:00", "23:50:00",
"23:51:00", "23:52:00", "23:53:00", "23:54:00", "23:55:00", "23:56:00",
"23:57:00", "23:58:00", "23:59:00"), class = "factor")
答案 0 :(得分：0)
使用[[代替[，它会起作用：
file[[2]] <- strptime(file[[2]], "%X")
结果：
[1] "2014-06-04 17:24:00" "2014-06-04 17:25:00"
[3] "2014-06-04 17:26:00" "2014-06-04 17:27:00"
[5] "2014-06-04 17:28:00" "2014-06-04 17:29:00"
顺便说一下，"%X"是"%H:%M:%S"的替代方案。