adding an int element into an associative array

hello,

i would like to create an associative array, to count how many nb of commande of the same number appears:
FOR
{% set cle = '' ~ commande %}
{% set dossiers = dossiers | merge({ (cle): (dossiers[cle] | default(0)) + 1 }) %}
ENDFOR
but the key is 0,1,2 instead of 353,832,156

how to resolve this problem ?

thanks