Description Usage Arguments Details Value Examples

When topic names and corresponding years are given, this function computes
the rise and fall trend during the period by `lm`

.

1 | ```
topic_trend(year, topic, relative = FALSE, zero = 0)
``` |

`year` |
a numeric vector of years for corresponding topics,
if it is not numeric, the function will try to
coerce. The years should be written in full-digit, that is, if they are 1998 and 2013,
do not simply write 98 and 13. No |

`topic` |
a character vector of topics. If it is not character, the function will
try to coerce. The length of topic and year should be the same. No |

`relative` |
if |

`zero` |
this can only be 0 (default) or |

The detail of trend info in the result is as follows:

(1) trendIndex: a regression with function

`lm`

is done for every topic with year as x and amount of topics as y. The value of trendIndex is the slope k in y = kx+b.(2) trendLevel: the p value of k.

(3) totalTrend: if trendIndex is larger than 0, then "rise", otherwise "fall". If trendLevel is smaller than 0.05, than "significant rise" or "significant fall".

(4) maxminYear: if totalTrend is "rise" or "significant rise", then this value points out which year has the largest amount. If several years have the largest value, the most recent year is returned. If totalTrend is "fall" or "significant fall", the year has the smallest amount is returned.

(5) detailTrend: if totalTrend is "rise" or "significant rise", then the function will see whether the year has the largest amount is the last year, if it is, then "rise along", otherwise "rise and fall". If totalTrend is "fall" or "significant fall", the function will see whether the year has the smallest amount is the last year, if it is, then "fall along", otherwise "fall and rise".

(6) simpleTrend: it is simply whether the amount of the last year is larger than that of the first year. If yes, then "rise", if smaller, then "fall", if the same, then "equal".

When computing trend for a topic, if less than 3 years has valid value and value
in other years are all `NA`

, then trendIndex, trendLevel and
maxminYear will be -999, and other cells are "less than 3y". If the numbers of a topic do not
change through years, then trendIndex will be 0, trendLevel and maxminYear will be -999, totalTrend
and detailTrend will be "almost same".

a list. The 1st element is trend info. The 2nd is a summary of amount
of each topic in each year. If argument relative is `TRUE`

, a 3rd
element is returned, which is the relative value (percentage) of each
topic in each year.

1 2 3 4 5 6 7 | ```
set.seed(1)
topic <- sample(c("art", "economy", "law", "politics", "sociology"), 50, replace = TRUE)
set.seed(2)
year <- sample(2011: 2016, 50, replace = TRUE)
tr1 <- topic_trend(year, topic)
tr2 <- topic_trend(year, topic, zero = NA)
tr3 <- topic_trend(year, topic, relative=TRUE)
``` |

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