To come across 與 To come by 的差別

To come across 與 To come by

To come across 後面多半指人或事物，是意外碰到(To meet someone or something by chance)

例如：
I came across Mr. Lucario, my former colleague, at the store yesterday.
昨日我在商店內碰到老同事Lucario先生。

He felt a little bit awkward when he came across his ex during a social function.
他再次社交活動中意外碰到前妻，感到有些尷尬。

How did you come across such a valuable photo of your family?
你怎麼找到這麼寶貴的家庭合照？

Mr. Lucario has recently come across some rare books at a flea market.
Lucario先生偶爾在跳蚤市場找到幾本罕見的書

To come by 是指獲得或取得(To get or to obtain)(句子後面多半跟事物)

例如：

How did you come by such a good-paying job?
你怎麼取得這份這麼高薪工作？

Mr. Lucario has come by a beautiful painting at an auction.
Lucario 先生在拍賣場獲得一幅漂亮的畫。

Be patient; you will soon come by an opportunity to publish your articles.
耐心點！你很快就有機會發表你的傑作。