Angular2 ng为了保存变量，迁移Twig

Question

I'm converting some PHP Twig templates into a new Angular5 project, and I'm stuck on how to handle a simple loop.

In my original Twig template, I have a series of data I loop through that includes a Month column. The data is already sorted by month, and I use this to create a header for each month in the loop by saving the variable, like:

{% set savedMonth = '' %}
{% for result in results %}
    {% set thisMonth = result.month %}
    {% if savedMonth != thisMonth %}
        <tr bgcolor='#c0c0c0'>
            <td colspan='5' align='left'>{{ thisMonth }}</td>
        </tr>
        {% set savedMonth = thisMonth %}
    {% endif %}
    <tr>
        <td valign='top' align='left'><a href='{{ path("app_view_index", { 'id': doc.id }) }}'>{{ doc.id }}</a></td>

    </tr>
{% endfor %}

This is a simplified example but you can see we look for a field change so I can insert my color row with the month at the start of each change.

Now I'm attempting to do the same thing in Angular5, but I can't figure out how to loop with *ngFor and do this kind of save. Is it even possible?

<tr *ngFor="let result of searchResults">
  <td align="left" class="home"><a [routerLink]="['/view', result.id]">{{ result.id }}</a></td>
  <td align="left" class="home">Subjects here</td> 
</tr>

Answer 1

Actually after some playing around I got a working version

in .ts

savedMonth: string;

changedMonth(month: any | string) {
 if (this.savedMonth === month) {
   return false;
  } else {
   this.savedMonth = month;
  return true;
 }
}

in template:

<ng-container *ngFor="let result of searchResults">
   <tr *ngIf="changedMonth(result.month)" bgcolor='#c0c0c0'>
       <td colspan='5' align='left'>{{ result.month }} </td>
    </tr>
    <tr>
       <td align="left" class="home"><a [routerLink]="['/view', result.id]">{{ result.id }}</a></td>         
    </tr>
  </ng-container>