Add observations to grids add 0 if not given

Question

I followed the following post: Aggregate values in raster using SF

points <- st_as_sf(SPDF_Violence["dummy"], coords = c("longitude", "latitude"),
                   proj4string =CRS("+init=epsg:4326 +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84"))


pointsID <- st_join(grid, points)

pointsID <- pointsID %>% 
  as.data.frame() %>% 
  group_by(ID) %>% 
  summarize(best1 = sum(dummy))
A<- left_join(grid, pointsID, by = "ID")

This is the code I use to join the points to the grids. My Question is now, how can I add the value of 0 to those grids, where I don't have any observations in my Dataframe A?

Thanks for your help! (sorry for not providing any reproducible Data, but I just don't know how should publish df big like that: maybe the structure of the Datasets helps:

s

structure(grid)
Simple feature collection with 579 features and 13 fields
Geometry type: GEOMETRY
Dimension:     XY
Bounding box:  xmin: 33.00154 ymin: 3.398829 xmax: 47.95823 ymax: 14.84548
CRS:           +proj=longlat +proj +ellps=WGS84 +datum=WGS84 +no_defs
First 10 features:
     ID ID_0 ISO   NAME_0 ID_1      NAME_1 HASC_1 CCN_1 CCA_1    TYPE_1 ENGTYPE_1 NL_NAME_1
312 312   74 ETH Ethiopia    1 Addis Abeba  ET.AA     0    14 Astedader      City      <NA>
342 342   74 ETH Ethiopia    1 Addis Abeba  ET.AA     0    14 Astedader      City      <NA>
315 315   74 ETH Ethiopia    2        Afar  ET.AF     0    02     Kilil     State      <NA>
344 344   74 ETH Ethiopia    2        Afar  ET.AF     0    02     Kilil     State      <NA>
345 345   74 ETH Ethiopia    2        Afar  ET.AF     0    02     Kilil     State      <NA>
346 346   74 ETH Ethiopia    2        Afar  ET.AF     0    02     Kilil     State      <NA>
374 374   74 ETH Ethiopia    2        Afar  ET.AF     0    02     Kilil     State      <NA>
375 375   74 ETH Ethiopia    2        Afar  ET.AF     0    02     Kilil     State      <NA>
376 376   74 ETH Ethiopia    2        Afar  ET.AF     0    02     Kilil     State      <NA>
404 404   74 ETH Ethiopia    2        Afar  ET.AF     0    02     Kilil     State      <NA>
                                              VARNAME_1                       geometry
312 Āddīs Ābaba|Addis Ababa|Adis-Abeba|Ādīs Ābeba POLYGON ((38.8761 8.898886,...
342 Āddīs Ābaba|Addis Ababa|Adis-Abeba|Ādīs Ābeba POLYGON ((38.77125 9.098195...
315                                                <NA> POLYGON ((40.12328 8.898884...
344                                                <NA> POLYGON ((40.00154 9.006727...
345                                                <NA> POLYGON ((40.50154 9.376003...
346                                                <NA> POLYGON ((40.64428 9.398895...
374                                                <NA> MULTIPOLYGON (((39.87534 9....
375                                                <NA> POLYGON ((40.00154 9.732064...
376                                                <NA> POLYGON ((40.96569 9.898848...
404                                                <NA> POLYGON ((40.00154 9.9927, ...

structure(points)
Simple feature collection with 59 features and 1 field
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 34.53333 ymin: 3.536615 xmax: 44.27806 ymax: 12.41674
CRS:           +proj=longlat +datum=WGS84 +no_defs
# A tibble: 59 x 2
   dummy            geometry
   <dbl>         <POINT [°]>
 1     1 (43.55722 8.220556)
 2     1  (39.0531 3.536615)
 3     1 (35.59728 9.370403)
 4     1 (38.08333 4.883333)
 5     1          (38.6 7.2)
 6     1  (42.08132 9.33658)
 7     1 (39.59622 11.82968)
 8     1     (37.85 8.98333)
 9     1 (41.56037 9.397441)
10     1         (38.95 8.3)