"Doublets"

5 Now Joseph had a dream, and when he told it to his brothers they hated him even more. 6 He said to them, “Hear this dream that I have dreamed: 7 Behold, we were binding sheaves in the field, and behold, my sheaf arose and stood upright. And behold, your sheaves gathered around it and bowed down to my sheaf.”...9 Then he dreamed another dream and told it to his brothers and said, “Behold, I have dreamed another dream. Behold, the sun, the moon, and eleven stars were bowing down to me.” (Gen 37:5-7,9).

5 And one night they both dreamed—the cupbearer and the baker of the king of Egypt, who were confined in the prison—each his own dream, and each dream with its own interpretation (Gen 40:5).

After two whole years, Pharaoh dreamed that he was standing by the Nile, 2 and behold, there came up out of the Nile seven cows, attractive and plump, and they fed in the reed grass. 3 And behold, seven other cows, ugly and thin, came up out of the Nile after them, and stood by the other cows on the bank of the Nile. 4 And the ugly, thin cows ate up the seven attractive, plump cows. And Pharaoh awoke. 5 And he fell asleep and dreamed a second time. And behold, seven ears of grain, plump and good, were growing on one stalk. 6 And behold, after them sprouted seven ears, thin and blighted by the east wind. 7 And the thin ears swallowed up the seven plump, full ears. And Pharaoh awoke, and behold, it was a dream (Gen 41:1-7).

i) Traditionally, liberal scholars regard "doublets" as evidence for independent traditions which redactors edited into a single narrative. However, many of the "doublets" are clearly integral to the narrative. So that's a bad explanation. 

ii) More recently, scholars like Robert Alter regard "doublets" as literary devices. That suggests fictional conventions. 

iii) There is, however, a realistic explanation. The reason Joseph and Pharaoh both receive two related dreams is to confirm the message. Two different ways to say the same thing. It's similar to Peter's threefold vision, which is reiterated to lend certainty to the disclosure:

9 The next day, as they were on their journey and approaching the city, Peter went up on the housetop about the sixth hour to pray. 10 And he became hungry and wanted something to eat, but while they were preparing it, he fell into a trance 11 and saw the heavens opened and something like a great sheet descending, being let down by its four corners upon the earth. 12 In it were all kinds of animals and reptiles and birds of the air. 13 And there came a voice to him: “Rise, Peter; kill and eat.” 14 But Peter said, “By no means, Lord; for I have never eaten anything that is common or unclean.” 15 And the voice came to him again a second time, “What God has made clean, do not call common.” 16 This happened three times, and the thing was taken up at once to heaven (Acts 10:9-16).

Emphatic repetition underscores the revelatory, authoritative nature of the dream or vision. It's not a fluke or coincidence. Rather, there's a pattern. 

iii) The dreams of the baker and cupbearer aren't doubled. They have one dream apiece. Two dreamers. That's a "doublet" of sorts, but it has a different function. To begin with, their coordinated dreams indicate special providence. God sent and synchronized their dreams. In addition, the two dreams forecast divergent fates for the two dreamers. And the survivor belatedly brings Joseph to Pharaoh's attention.