Expressing "one by one" with "yi"
The expression "one by one" is also simple in Chinese (you don't even need the word "by"), except that it gets complicated somewhat by the concept of measure words.
Used as "One by One"
The most obvious way to express "one by one" is 一个一个 (yī gè yī gè), and this expression is, in fact, quite common, especially when referring to people doing things one by one. But other measure words can be used in the same pattern as well.
一 + Measure Word + 一 + Measure Word (+ Noun)
- 别 吵 ，一 个 一 个 说。Don't argue. Speak one by one.
- 别 着急 ，一 点 一 点 做 。Don't worry, do it little by little.
- 请 一 个 房间 一 个 房间 检查 。Please inspect room by room.
- 别 拿 那么 多 ，一 个 一 个 拿 。Don't carry so much. Pick them up one at a time.
Used as "Little by Little"
Aside from just meaning "one by one," when 一 (yī) is used with a measure word that is a unit of time like "day" or "year," the meaning changes to "little by little" ("day by day," "year by year") or "gradually."
一 + Time Unit + 一 + Time Unit (+ Noun)
- 宝宝 一 天 一 天 在 长大 。The baby is growing up day by day.
- 爸爸 妈妈 一 年 一 年 在 变 老 。Year by year, mom and dad are growing old.
Used as "Over and Over Again"
When a measure word phrase like "one time" is repeated, the meaning also changes. When using a verb measure word like 次 (cì) or 遍 (biàn), using this pattern can indicate how the action is performed or indicate repetition of the the action.
一 + [Measure Word] (+ 又) + 一 + [Measure Word]
If the speaker wants to emphasize that the action has been repeated many times, 又 (yòu) can add emphasis.
- 我 一 次 一 次 问，他 就是 什么 都 不 说 。I asked him again and again, but he just wouldn't say anything.
- 我 一 遍 一 遍 地 跟 他 解释，他 还是 不 听 。I explained it to him again and again, but he still won't listen.
- 你 为什么 一 遍 又 一 遍 地 听 这 首 歌 ？Why do you listen to this song over and over again?
- 他们 一 次 又 一 次 犯 这 种 小 错误 ，让 经理 很 头疼 。They keep making the same mistake over and over again, and it's giving their manager a headache.