Here are some links if you want to know more about the subject:

Assimilation in spanish

Assimilation test

Assimilations of the /j/

Phonetics and phonology blog

Another example in english:

Another example in spanish:

"Un perro"
"Un beso"

This phenomenon also occurs in Spanish

When he said: "Por lo tanto" he pronounced "po lo tanto".

Here are some examples of assimilation:

"Goodnight"

Assimilation examples

Consonant assimilation

In the case the two phonemes can fuse completely and give a birth to a different one.
This is also called "Coalescence"


Example Do you smoke?: In slower speech we might say: dju sməʊk. In fast, casual speech we could say: dʒu sməʊk.

Reciprocal assimilation

When both sounds (the assimilating and the assimilated one) under go changes.

Historically this has occurred in words like:

Soldier, picture or fissure.

where the reconstructable earlier pronunciation /‘soυldjər/, /‘pıktu:r/, /‘fısju:r/ has become /‘səυldзə/,/‘pıkt∫ə/, /fı∫ə/

In current colloquial English, similar assimilation occurs in phrases such as "What d’you want" /wt∫əwnt/ or
Could you?  /‘kυdZu:/.