I do not find this use of the English preposition in—namely, to denote identity—referred to in English dictionaries, though it ought to be.
The same mode of expressing existence by an or in is found in the Ulster and Scotch phrase for
to be alone, which is as follows, always bringing in the personal pronoun:—'I am in my lone,' 'he is in his lone,' 'they are in their lone'; or more commonly omitting the preposition (though it is always understood): 'She is living her lone.' All these expressions are merely translations from Gaelic, in which they are constantly used; 'I am in my lone' being from Tá me am' aonar, where am' is 'in my' and aonar, 'lone.' Am' aonar seal do bhiossa, 'Once as I was alone.' (Old Irish Song.) In north-west Ulster they sometimes use the preposition by:—'To come home by his lone' (Seumas Mac Manus). Observe the word lone is always made lane in Scotland, and generally in Ulster; and these expressions or their like will be found everywhere in Burns or in any other Scotch (or Ulster) dialect writer.
Prepositions are used in Irish where it might be wrong to use them in corresponding constructions in English. Yet the Irish phrases are continually translated literally, which gives rise to many incorrect dialect expressions. Of this many examples will be found in what follows.
'He put lies on me'; a form of expression often heard. This might have one or the other of two meanings, viz. either 'he accused me of telling lies,' or 'he told lies about me.'
'The tinker took fourpence out of that kettle,' i.e. he earned 4d. by mending it. St. Patrick left his name on the townland of Kilpatrick: that nickname remained on Dan Ryan ever since.
'He was vexed to me' (i.e. with me): 'I was at him for half a year' (with him); 'You could find no fault to it' (with it). All these are in use.
'I took the medicine according to the doctor's order, but I found myself nothing the better of it.' 'You have a good time of it.' I find in Dickens however (in his own words) that the wind 'was obviously determined to make a night of it.' (See p. [10] for a peculiarly Irish use of of it.)
In the Irish poem Bean na d-Tri m-Bo, 'The Woman of Three Cows,' occurs the expression, As do bhólacht ná bí teann, 'Do not be haughty out of your cattle.' This is a form of expression constantly heard in English:—'he is as proud as a peacock out of his rich relations.' So also, 'She has great thought out of him,' i.e. She has a very good opinion of him. (Queen's Co.)