The ornamental design for a collapsiblecompartment within a bag, as shown and described.
FIG. 1 is a perspective view of a collapsible compartment within a bag;
FIG. 2 is a top view of the collapsible compartment within a bag;
FIG. 3 is a bottom view of the collapsible compartment within a bag;
FIG. 4 is a front view of the collapsible compartment within a bag;
FIG. 5 is a rear view of the collapsible compartment within a bag;
FIG. 6 is a right side view of the collapsible compartment within a bag;
FIG. 7 is a left side view of the collapsible compartment within a bag; and,
FIG. 8 is a side view of the collapsible compartment within a bag with the collapsible compartment in the collapsed state, the right and left views being the same.
The broken lines showing a bag are for the purposes of illustrating environment and forms no part of the claimed design.